7. WHAT DO I LOOK FOR IN BUYING A NEW BATTERY?

Last Updated on July 24, 2004

INDEX:

7.1. Battery Types

7.1.1. Wet Standard (Sb/Sb)

7.1.2. Wet Low Maintenance (Sb/Ca)

7.1.3. Wet Maintenance Free (Ca/Ca)

7.1.4. VRLA AGM (Absorbed Glass Mat)

7.1.5. VRLA Spiral Wound AGM (Absorbed Glass Mat)

7.1.6. Wet Marine Starting

7.1.7. VRLA Gel Cell

7.1.8. What Are the Differences Between Car, Marine Starting and Deep Cycle Batteries?

7.1.9. What Are Dual or Multi-battery Systems?

7.2. CCA (Cold Cranking Amps)

CCA vs. Temperature Diagram

7.3. Reserve Capacity (RC) or Amp Hour (AH) Capacity

7.3.1. Is Capacity Effected By Temperature?

AH Capacity vs. Temperature Graph

7.3.2. How Do I Increase Battery Capacity?

Battery Wiring Diagrams

7.3.3. Which is Better, Two 6-volt Batteries in Series or Two 12-volt Batteries in Parallel?

7.3.4. How Do I Increase the Voltage?

7.3.5. How Can I Reduce the Voltage in Half?

7.3.6. Which Weighs More--One 12-volt or Two 6-volt Batteries?

7.3.7. Can I Mix Non-Identical Batteries?

7.4. Size

7.5. Terminals

7.6. Freshness

7.7. Warranty

7.8. Buying Tips

7.9. How Do I Size For Backup AC Power?

Car battery buying strategy for use in Germany, for example, is different than in the warmer climates found in Texas. In the colder climates, higher CCA (Cold Cranking Amp) ratings are more important. In a hot climate, higher RC (Reserve Capacity) or AH (Ampere Hour) ratings are more important than CCA; however, these ratings should meet or exceed your vehicle's OEM (Original Equipment Manufacturer) requirements. Do NOT buy a new battery until you need it because it will sulfate sitting in storage and you will lose capacity. Below is an example of car battery life expectancy in the United States from Interstate Batteries:

[Source: Interstate Batteries]

7.1. Battery Types

The two most common categories of car and deep cycle batteries are wet (also known as "flooded", "liquid electrolyte", "vented", or "VLA" cell) and Valve Regulated Lead-Acid (VRLA). Within the wet category, the three most common battery types are Standard (Sb/Sb), Low Maintenance (Sb/Ca) and Maintenance Free (Ca/Ca), which are defined in more detail below. In the VRLA category, there are AGM (Absorbed Glass Mat), spiral wound AGM, and Gel Cell lead-acid batteries. The one additional category for smaller (typically below 50 AH) deep cycle batteries is SLA (Sealed Lead Acid) using AGM or Gel Cell construction. They are sealed with a safety pressure relief valve or plug in case of excessive gas pressure build up due to overcharging.

When selecting a battery type, it is extremely important that you select one that will MATCH the voltage output of your charging system. The easiest way to accomplish this is to replace your battery with the same or compatible type of battery that originally was installed. If you change your replacement battery to another battery type, you might have to adjust the charging voltage to prevent undercharging or overcharging that could damage or reduce the service life of your new battery. For example, replacing an Original Equipment Manufacturer (OEM) wet sealed Maintenance Free (Ca/Ca) with a wet non-sealed Low Maintenance (Sb/Ca) battery (with filler caps) might cause the Low-Maintenance (Sb/Ca) battery to be slightly overcharged and consume more water. If you charge a Maintenance Free (Ca/Ca) battery with a charging system or charger designed for a Low Maintenance (Sb/Ca) battery (with filler caps), you could undercharge the Maintenance Free (Ca/Ca) battery. Replacing any other non-Gel Cell type of battery with a Gel Cell could overcharge it. When in doubt, replace with an AGM or spiral wound AGM battery. Ventilation is required for all lead-acid batteries and good ventilation is mandatory for wet batteries to dissipate the explosive gasses produced during charging.

Deep cycle batteries are broadly divided into motive and stationary applications. Motive applications are where the battery is discharged in operations that will consume between 20% and 80% of the battery's capacity and then recharged (which is considered to be one cycle). Some examples of motive (also known as "cycling" or "traction") applications are for batteries used in recreational vehicles (RV), motor homes, caravans, trailers, boats, wheelchairs, golf carts, solar, floor sweepers, folk lift trucks and other electric vehicles (EV) and typically have 200-500 cycles per year. Stationary (also known as "float", "reserve", "backup" or "standby") applications are where stationary batteries is used to provide backup or standby power during loss of the primary source of power such as uninterruptible power systems (UPS), emergency lighting systems, security systems, telecommunications systems, etc., and typically have 2-12 cycles per year. Generally, stationary batteries have longer service lives, more life cycles and cost more than motive batteries. The chargers for motive and stationary batteries are different as well.

Non-sealed wet Standard (Sb/Sb), wet Low-Maintenance (Sb/Ca), VRLA AGM or VRLA Gel Cell batteries with pasted, tubular or Manchester ("Manchex") positive plates or VRLA Spiral Wound AGM batteries are recommended for motive deep cycle applications. Non-sealed wet Standard (Sb/Sb), wet Low-Maintenance (Sb/Ca), wet Maintenance Free (Ca/Ca) batteries with pasted or solid (Planté) positive plates are recommended for stationary applications. For more information about larger deep cycle batteries (greater than 250 AH), please see Wind & Sun's Ultimate Deep Cycle Battery FAQ http://www.wind-sun.com/Batteries/Battery_FAQ.htm and Zen and the Art of Choosing a Deep Cycle Battery at http://www.windsun.com/Batteries/battery_comparison.htm

Wet deep cycle batteries, such as Marine/RV, leisure and some golf cart, that use pasted positive plates are less expensive to manufacturer and have few life cycles and shorter service lives at 50% average Depth-of-Discharge (DoD) level than the deep cycle batteries with solid (Planté), tubular or Manchester (or "Manchex") positive plates. They also have significantly fewer life cycles at the 80% average DoD level. Be aware that some starting battery manufacturers have added handles and stud type terminals to their cheaper starting batteries and sell them as Marine/RV deep cycle. The major disadvantage of VRLA (AGM or Gel Cell) deep cycle batteries are their high initial cost (up to three times over the cost of a wet Standard (Sb/Sb) batteries), but arguably can have an overall lower total cost of ownership due to a longer service life, no "watering" and other labor costs, and faster recharging. The total cost of ownership should be considered when buying deep cycle batteries.

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7.1.1. Wet Standard (Sb/Sb)

Standard or "Conventional" (Sb/Sb) non-sealed lead-acid batteries (with filler caps) have Lead-Antimony (Sb)/Antimony (Sb) plates and have been commercially available for almost 100 years. They have a:

• Tolerance for a wide range of charging current (to 25% of the battery's capacity) and voltage
  
  
• Long service live (if properly maintained)
  
  
• Increased water consumption
  
  
• Low tolerance for heat (they will lose half of their service life for every Increase of 15° F (8.3° C) over 80° F (26.7° C)
  
  
• High self discharge rate (depending on the temperature up to 50%-60% per month)
  
  
• Charging losses of 15%-20% and maximum continuous discharge rate 25% of their capacity
  

For these reasons, they have almost been completely replaced by wet Low Maintenance (Ca/Sb) batteries for high temperature underhood starting applications, but are still used for many deep cycle motive applications. Wet Standard (Sb/Sb) batteries are generally the least expensive lead-acid batteries.

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7.1.2. Wet Low Maintenance (Sb/Ca)

The wet (or "flooded" cell) Low Maintenance batteries (with filler caps) have a Lead-Antimony (Sb)/Calcium (Ca) dual alloy or hybrid plate formulations. They have most of the same characteristics as a wet Standard (Sb/Sb) batteries, except they can handle the high underhood heat better. Some battery manufacturers, such as Johnson Controls, build "North" and "South" car battery versions to make up for the differences in cold and hot climates. Some also construct special car batteries that have a higher tolerance to heat by changing plate or connecting strap formulations or providing for more electrolyte. For off road applications in trucks, recreational vehicles (RVs), motor caravans, 4x4s, vans or SUVs (Sport Utility Vehicles), some battery manufacturers build "high vibration", "heavy duty", "commercial", or "RV" battery versions designed to reduce the effects of moderate vibration. A wet Low Maintenance (Sb/Ca) battery will typically cost a little more than a similar sized wet Standard (Sb/Sb) battery.

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7.1.3. Wet Maintenance Free (Ca/Ca)

Wet Maintenance Free batteries have a Lead-Calcium (Ca)/Calcium (Ca) plate chemistry or formulation, for example, Delphi's ACDelco. The advantages of Maintenance Free (Ca/Ca) batteries over Low Maintenance (Sb/Ca) are:

• Less preventive maintenance due to less water loss
  
  
• Greater overcharge resistance
  
  
• Reduced terminal corrosion
  
  
• Up to 400% less self discharge
  
  
• Less risk to consumers because there is less to service

However, they are more prone to deep discharge ("dead" or "flat" battery) failures due to increased shedding of active plate material and development of a barrier layer between the active plate material and the grid metal. If a Maintenance Free (Ca/Ca) battery is sealed, water can not be added when required. For that reason, in hot climates, using non-sealed wet batteries (with filler caps), so you add distilled water, for under the hood or a sealed AGM battery inside the passenger compartment or trunk is highly encouraged for longer battery service life. Wet Maintenance Free (Ca/Ca) batteries are generally more expensive than wet Low Maintenance (Sb/Ca) batteries.

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7.1.4. VRLA AGM (Absorbed Glass Mat)

Sealed Absorbed Glass Mat (AGM) batteries (also know as "starved electrolyte") have a very fine fiber Boron-Silicate glass mat between their plates. They have all of the advantages of the Maintenance Free (Ca/Ca) batteries plus:

• Safer (due the much lower production of hydrogen gas during charging)
  
  
• Do not require water
  
  
• Lower self-discharge rate (typically 1%-2% per month)
  
  
• Longer service life
  
  
• Higher resistance to vibration
  
  
• Lower deep discharge failure
  
  
• Higher bulk charge acceptance rate (which means up to a 15% shorter recharge time)
  
  
• Withstand heat better
  
  
• Do not require special hazardous shipping and can be used near salt water
  
  
• Spill proof and can be mounted in virtually any position (because they are sealed)
  
  
• Charging losses of 4% and maximum continuous discharge rate 33% of their capacity
  
  
• Can be used inside a semi-enclosed area, like the passenger compartment or trunk
  
  

Relocating the vehicle's starting battery to the passenger compartment is becoming more popular because vehicle manufacturers want to extend their "bumper-to-bumper" warranty periods, to avoid underhood temperature extremes, to provide more weight in the rear, or to save underhood space. They use GRT (Recombinant Gas Technology), which simply means the gasses are recombined back into water during recharging and contained within each cell. AGM batteries are more expensive than Maintenance Free (Ca/Ca) batteries. Some AGM batteries, for example Concorde, can be equalized. They will accept all the power that a charging system will produce. This means if you are using an alternator sized at 25% (or less) of the capacity of the battery bank, it possible to over heat an air cooled alternator and burn it up during a long bulk charging phase. For large capacity battery banks, using a high output alternator, voltage regulator with an alternator temperature sensor or water cooled alternator is highly recommended.

You can expect AGM car batteries to the $80 to $120 range as more competition occurs. Examples of sealed AGM batteries are Concorde's Lifeline, Delphi's Freedom Extra, Hawker's Odyssey, New Castle, and ACDelco's Platinum. An AGM battery can normally replace a wet Low Maintenance (Sb/Ca) or Maintenance Free (Ca/Ca) battery, but a wet Low Maintenance (Sb/Ca) battery normally cannot replace an AGM battery without adjusting the charging voltages. Expect to see 36-volt AGM car batteries with 14/42-volt dual or 42-volt electrical systems offered by some of the premium car manufacturers starting in the 2003 model year. In the near term, you should expect to see more sealed AGM batteries replacing wet lead-acid batteries. Longer term, Lithium Ion (LiIon) batteries will used in hybrid automotive applications, which will eventually be replaced by fuel cells in the next 10-20 years.

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7.1.5. VRLA Spiral Wound AGM (Absorbed Glass Mat)

For excessive vibration applications, in off-road operation, or extreme conditions, it is best to use a spiral wound VRLA (Valve Regulated Lead-Acid) AGM battery because there is no shedding of active plate material since the plates are immobilized. In addition, they use GRT (Recombinant Gas Technology) and have all of the characteristics of the VRLA AGM batteries plus:

• Smaller
  
  
• Recharges faster
  
  
• Wider range of charging voltages
  
  
• Charging losses of 4% and maximum continuous discharge rate 33% of their capacity
  
  

Examples of spiral wound VRLA AGM batteries are Johnson Controls', Optima, Exide's Select Orbital, or Hawker's Cyclon. Typically spiral wound AGM car batteries cost between $90 and $150 and deep cycle versions cost more.

SPIRAL WOUND AGM BATTERY

[Source: Optima]

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7.1.6. Wet Marine Starting

A wet "Dual" or Marine Starting battery is a compromise between a car and deep cycle battery that is specially designed for high vibration in marine applications. A Marine Starting battery can have wet Standard (Sb/Sb), wet Low Maintenance (Sb/Ca), wet Maintenance Free (Ca/Ca) or VRLA AGM plate formulations. But, please beware of Marine Starting and deep cycle batteries that are cheap. They are often car batteries with handles and stud or combination terminals. A deep cycle or "Dual Marine Starting" battery will work as a starting battery if it can produce enough current to start the engine. Good ventilation is required for all wet (or "flooded") deep cycle batteries to dissipate the gasses produced during charging. For saltwater applications, sealed AGM (or Gel Cell) should be only used to prevent the formation of DEADLY chlorine gas when battery electrolyte is mixed with salt water.

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7.1.7. VRLA Gel Cell

Sealed VRLA (Valve Regulated Lead-Acid) Gel Cell batteries use GRT (Recombinant Gas Technology) and use a thickening agent like fumed silica gel to immobile the electrolyte instead of a liquid electrolyte like the wet batteries. They have a lot of the same advantages of AGM batteries. When comparing Gel Cell to AGM and Spiral Wound AGM batteries, Gel Cells will typically:

• Greater ability to withstand a deep discharge, but not temperatures over over 100°F (37.8° C) because of the possibility of "thermal runaway"
  
  
• 10 to 15 cycle preconditioning or "break-in" period
  
  
• Less Cold Cranking Amps
  
  
• 80% of the capacity of a similar sized AGM battery and physically larger
  
  
• Slower recharging times and intolerant of higher charging voltages
  
  
• Lower capacity in cold temperatures
  
  
• Up to 20% more life cycles
  
  
• Costs more to manufacture
  
  
• Charging losses of 4% and maximum continuous discharge rate 25% of their capacity
  
  

The ideal ambient temperature for a Gel Cell battery is 72° F (22.2° C). Examples of Gel Cell batteries are Sonnenschein, East Penn, MK, Exide, etc.

For some considerations of replacing flooded batteries with Gel Cell or AGM batteries, please read David Eidell's IMPORTANT NOTE ABOUT THE SUITABILITY OF ABSORPTIVE GLASS MAT (AGM) AND GELLED ELECTROLYTE BATTERIES IN RV'S at http://www.rversonline.org/ArtAGM.html For a more detailed comparison, read an article written by Constian von Wentzel, Comparing Marine Battery Technologies. at http://www.vonwentzel.net/Battery/index.html For more technical information on VRLA batteries, please visit Oerlikon Battrie's Lead Acid Batteries VRLA Types at http://www.accuoerlikon.com/html/accud02.htm

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7.1.8. What Are the Differences Between Car, Marine Starting and Deep Cycle Batteries?

Car batteries are specially designed with thinner (.04 inch or 1.02 mm) and more porous plates for a greater surface area to produce the high amps required to start an engine. They are engineered for up to 5,000 shallow (to 3%) discharges, which works out to over four engine starts per day. Car batteries should NOT be discharged below 90% State-of-Charge. They use sponge lead and expanded metal grids rather than solid lead. Marine Starting batteries are a comprise between a car and deep cycle battery and are designed for starting and prolonged discharges at lower amperage that typically consumes between 20% and 50% of the battery's capacity. Motive and Stationary deep cycle batteries have much thicker (up to .25 inch or 6.35 mm) plates, more lead, and weight more than car batteries the same size. They are normally discharged between 20% and 80% at lower amperage. deep cycle batteries will typically outlast two to ten car batteries in a deep cycle application.

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7.1.9. What Are Dual or Multi-battery Systems?

For RVs, motor homes, caravans, boats, and other large vehicles, both car and deep cycle batteries are often used. A car battery is normally used to start the engine and Motive deep cycle (or leisure) batteries that are the same type as the car battery are used to power the electrical accessories. The batteries are connected to a diode isolator (or combiner), dual output alternator, or A/B switch to keep the starting battery from becoming discharged when using the deep cycle batteries. When the charging system is running, the batteries are automatically recharged (except with the manual A/B switch) with most of the current flowing to the battery with the lowest State-of-Charge. Ralph Scheidler at Sure Power has written an excellent, easy to understand, free e-booklet, Introduction to Batteries and Charging Systems, about multi-battery applications. It is available online at http://www.surepower.com/pdf/ebr_int.pdf. A common deep cycle application in recreational vehicles is using a DC to AC inverter, which is used to convert 12 VDC to 120 (or 240) VAC power. It takes between 12 and 14 amps of 12-volt DC power to make one amp (or 120 watts) of 120 VAC power (or one-half amp or 120 watts of 240 VAC power), so deep cycle batteries or vehicle charging systems should be used to power inverters and NOT starting batteries. Some multi-battery systems can get extremely complex as evidenced by the wiring diagram near the end of Tor Pinney's article, THE INTEGRATED ENERGY SYSTEM, The Optimum Electrical Power System for the Cruising Sailboat found at http://www.anchoryachts.com/articles/energy.htm.

Some of the following risks are undertaken when a discharged deep cycle battery (or bank) is connected in parallel to the starting battery without using a diode isolator:

• If a discharged deep cycle battery (or bank) is connected to a charged starting battery in parallel, a large current could flow from the starting battery to the deep cycle battery in an attempt to equalize the voltage. Over time, deeply discharging the starting battery could prematurely kill it. This can discharge the starting battery to the point that the engine can not be started.
  
  
• If the wiring or contacts of the isolation relay or switch are not heavy enough to carry the current, damage could occur.
  
  
• If hydrogen is present, an explosion could occur due to the arc created by the relay or switch closure.
  
  
• If the charging system has insufficient capacity, a large deep cycle battery (or bank), especially a AGM VRLA, could accept all the output of the charging system and overheat the alternator causing it to fail or not fully recharge the starting battery.
  
  
• If the connection is not switched, either the deep cycle battery (or bank) is not charged or the starting battery will be discharged.
  
  

Regardless of what isolation method is used, the correct battery manufacturer's temperature compensated charging voltages need to be applied directly across the respective battery terminals to optimize the battery's capacity and overall service life. If the voltages are not correct, then battery under or overcharging can occur, so it is important to try and use the same battery types (plate chemistries).

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7.2. CCA (Cold Cranking Amps)

If the battery is to used in a starting application, Cold Cranking Amps (CCA) is the second most important consideration; otherwise, for non-starting deep cycle applications, please skip this section and go to Section 7.3. Reserve Capacity (RC) or Amp Hour (AH) Capacity. The battery's CCA rating should meet or exceed, your vehicle's OEM cold cranking requirement, for your climate. CCA is the discharge load measured in amps that a new, fully charged battery, operating at 0° F (-17.8° C), can deliver for 30 seconds and while maintaining the voltage above 7.2 volts. car and Marine Starting batteries are sometimes advertised by their CA (Cranking Performance Amps) measured at 32° F (0° C), MCA (Marine Cranking Amps) measured at 32° F (0° C), or HCA (Hot Cranking Amps) measured at 80° F (26.7° C). These measurements are not the same as CCA. Do not be misled by the higher CA, MCA or HCA ratings. To convert CA or MCA to CCA, multiply the CA or MCA by 0.8. To convert HCA to CCA, multiply HCA by 0.69.

To start a four cylinder gasoline engine, you will need approximately 600-700 CCA; six cylinder gasoline engine, 700-800 CCA; eight cylinder gasoline engine, 750-850 CCA; three cylinder diesel engine, 600-700 CCA; four cylinder diesel engine, 700-800 CCA; and eight cylinder diesel engine, 800-1200 CCA. Bruce Bowling and Al Grippo have written a very handy Battery Cold-Cranking Amp Estimation calculator which can be found at http://www.bgsoflex.com/cca.html. To convert CCA, a SAE (Society of Automotive Engineers) standard, to an EN (now known as ETN), IEC, DIN or JIS standard, please refer to the Conversion Table at http://www.midtronics.com/manuals/power_sensor105_manual.pdf from Midtronics.

In hot climates, buying car or Marine Starting batteries with double or triple the cold cranking amps that exceeds your starting requirement is a waste of money because the extra amps will not be used. A starter motor will only demand what it needs to operate. However, in cold climates a higher CCA rating is better, due to increased power required to crank a sluggish engine and the inefficiency of a cold car battery and the demand is greater. As car batteries age, they are also less capable of producing as much CCA as when they were new. According to the BCI (Battery Council International), diesel engines require 220% to 300% more current than their gasoline counterparts and winter starting requires 140% to 170% more current than the summer. These increased requirements are accounted for in the OEM (Original Equipment Manufacturer) CCA recommendation.

CCA vs. TEMPERATURE

[Source: Exide]

If more CCA capacity is required, two identical larger 6-volt starting batteries can be connected in series or two identical 12-volt starting batteries can be connected in parallel. Please refer to the diagrams in Section 7.3 below for more information about connecting batteries in series and parallel. If you connect two 12-volt batteries in parallel and they are identical in type, age and capacity, you can potentially double your original capacity. If you connect two that are not the same type, you will either overcharge the smaller (or older) of the two or you will undercharge the larger (or newer) of the two.

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7.3. Reserve Capacity (RC) or Amp Hour (AH) Capacity

For car batteries, the third most important consideration is the Reserve Capacity (RC) or Amp Hour (AH) Capacity ratings because of the effects of increased parasitic (ignition key off) loads while long term parking and emergencies. RC is the number of minutes a fully charged battery at 80° F (26.7° C) can be discharged at a constant 25 amps until the voltage falls below 10.5 volts. European and Asian starting and deep cycle batteries are usually rated in Amp Hours (AH). To convert RC to AH (or AH to RC), check the battery manufacturer's specifications. More RC is better in every case. In a hot climate, if your car has a 360 OEM cold cranking amps requirement, then a 400 CCA rated battery with 120 minutes of RC and more electrolyte for cooling would be more desirable than one with 600 CCA with 90 minutes of RC. There is also a relationship between the weight of the battery and the amount of RC (or AH).

For deep cycle batteries, an important consideration is that the Ampere-Hour (AH) rating will meet or exceed the requirements based on your application and how much weight you can carry. Most deep cycle batteries are normally rated in number of hours it take to discharge a fully charged battery to 10.5 volts in 20 hours at 80° F (26.7° C), denoted as "C/20". Discharge rates of 100 hours (C/100), 10 hours (C/10), 8 hours (C/8) or 6 hours (C/6) are also common ratings. The higher the discharge rate (or lower number of hours), the lower the capacity due to the Peukert Effect and the internal resistance of the battery. (Please see Section 9.8.). Within a BCI Group Size, the battery with higher AH (or RC) will tend to larger in physical size, have longer lives and weigh more because of thicker plates and more lead.

Normally the best buy will be the heaviest battery that best suites your application and that has the lowest cost (including maintenance) for the total amount of power it will produce over it's service life.

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7.3.1. Is Capacity Effected By Temperature?

Temperature does matter! The following graph from Concorde shows the effects of temperature on the capacity on their AGM battery:

PERCENT CAPACITY vs. TEMPERATURE

[Source: Concorde]

7.3.2. How Do I Increase Battery Capacity?

If more amp hours (AH) or Reserve Capacity (RC) are required, there are normally three ways to accomplish this:

7.3.2.1. Two identical larger capacity six-volt batteries can be connected in series (POSITIVE (+) terminal of Battery One to the NEGATIVE (-) terminal of Battery Two).

12 Volts Series

[Source: Yacht Outfitting]

7.3.2.2. Two (or more) identical 12-volt batteries can be connected in parallel. If you connect two 12-volt batteries in parallel and they are identical in type, age and capacity, you can potentially double you original capacity. If you connect two that are not the same type or capacity, you will either overcharge the smaller of the two, or you will undercharge the larger of the two. Please take special note of the POSITIVE (+) connection and NEGATIVE (-) connection to the load or charger and limit the number of batteries (or strings of batteries) in parallel to four.

12 Volts Parallel

[Source: Yacht Outfitting]

7.3.2.3. Two identical larger capacity six-volt batteries can be connected in series (POSITIVE (+) terminal of Battery One to the NEGATIVE (-) terminal of Battery Two) to make a "12-volt battery". Two (or more) identical "12-volt batteries" can be connected in parallel. The combination is referred to as a series-parallel connection. Please take special note of the POSITIVE (+) connection and NEGATIVE (-) connection to the load or charger and limit the number of batteries (or strings of batteries) in parallel to four.

12 Volts Series-Parallel

[Source: Yacht Outfitting]

Additional information on deep cycle battery bank sizing can be found at http://www.glacierbay.com/1batcrg.htm in an article written by the folks at Glacier Bay Refrigeration or by Constian von Wentzel at http://www.vonwentzel.net/Battery/02.Size/index.html.

When connected as exactly shown in the diagrams, the batteries will discharge and charge equally. Between the batteries, cable lengths should be an equal length, short as possible and sized large enough to prevent significant voltage drop of 0.075 volts (75 millivolts) per 100 amps or less in the cables and connectors. Battery cables to the charger or inverter should be an equal length so the batteries will charge or discharge evenly. What is important is that the battery manufacturer's recommended charging voltages are being applied across the battery's terminals from the charging source. Using an adjustable Low Voltage Disconnect set to a minimum of 10.5 VDC (12.0 VDC is better) will insure a higher average Depth-of-Discharge and will protect electrical and electronic appliances and the batteries from damage from a real deep discharge.

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7.3.3. Which is Better, Two 6-volt Batteries in Series or Two 12-volt Batteries in Parallel?

Some battery experts believe that batteries in series are easier to discharge or charge because the same amount of current is applied to each cell and are a little more reliable. Other battery experts believe that batteries in parallel are better because they require less space, will have more capacity due to the Peukert Effect and if a cell should fail, the bad battery can be disconnected and the other one can continued to be used. For additional information on this discussion, please read Battery Configuration: Parallel or Series? published by Sierra Nevada Airstreams at http://sierranevadaairstreams.org/.

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7.3.4. How Do I Increase the Voltage?

If more voltage is need, connect identical batteries in series in the following manner:

24 Volts Series

[Source: Yacht Outfitting]

Two identical 12-volt batteries can be connected in series to produce 24-volts. Three identical 12-volt batteries connected in series or six identical six-volt batteries will produce 36-volts. Note that the amp hour capacity remains the same.

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7.3.5. How Can I Reduce the Voltage in Half?

"Half-tapping" two batteries in series can be used to produce half of the voltage. For example, let's assume that two identical 12-volt batteries are used in series to power a 24-volt trolling motor and there is a requirement to power 12-volt lights or electronic equipment. The 12-volt electrical appliances can be connected to the 12-volt batteries as long the 12-volt electrical loads are equally divided between the two 12-volt batteries, so the loads are balanced, separate positive and negative wiring, and isolated from ground. You could also use a 24-volt to 12-volt DC-to-DC Converter or a separate 12-volt charging system and battery to produce 12-volts.

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7.3.6. Which Weighs More--One 12-volt or Two 6-volt Batteries?

Of equal AH capacity, a single 12-volt battery will weigh approximately 10% less than two six-volt batteries connected in series due to the additional case material and the battery connecting cable. But, the two six-volt batteries can be split a part and each battery weighs approximately half of the weight of the 12-volt battery.

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7.3.7. Can I Mix Non-Identical Batteries?

To prevent charging problems when connecting batteries in series, parallel, or series-parallel, do not mix old and new batteries or ones of different capacities or types. Mixing old batteries with new batteries is like mixing old milk with new milk--soon you have nothing but old milk. The reason is because you will either undercharge the larger (or newest) of the batteries or overcharge the smaller (or oldest) of the batteries.

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7.4. Size

In North America, manufacturers build their batteries to an adopted Battery Council International (BCI) Group Size Number (U1, 24, 27, 31, 34, 35, 65, 75, 78, 8D, GC, L-16, etc.) standard (http://www.rtpnet.org/~teaa/bcigroup.html). These specifications, which are based on the physical case size, terminal placement, type and polarity. In Europe, the ETN (European Type Numbering) standard has replaced the older EN, IKC, Italian CEI, and German DIN standards. In Asia, the Japanese JIS standard is commonly used. The OEM battery number is a good starting place to determine the replacement battery. Within a size, the CCA and RC ratings, warranty and battery type will vary within models of the same brand or from brand to brand. Batteries are generally sold by model or series, so the size numbers will vary for the same price. For the same price, you can potentially buy a physically larger battery with more CCA or RC (or AH) than the battery you are replacing. For example, a 34/78 group might replace a smaller 26/70 group and give you an additional 30 minutes of RC. If you buy a physically larger battery, be sure that the replacement battery will fit, the cables will connect to the correct terminals, and that the terminals will NOT touch metal surfaces such as the hood when it is closed.

The battery manufacturers publish application selection guides that contain OEM cold cranking amperage requirements and group number replacement recommendations by make, model and year of car, battery size, and CCA and RC (or Amp Hour) specifications. You can also find the BCI size information online at http://www.rtpnet.org/~teaa/bcigroup.html or in some of the selection guides in the Battery Manufacturers and Private Labels List found at http://www.batteryfaq.org/. Manufacturers might not build or the store might not carry all the battery sizes. To reduce inventory costs, dual terminal "universal" batteries that will replace several group sizes are becoming more popular and fit 75% or more of cars on the road today.

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7.5. Terminals

There are six types of common battery terminals: SAE Post, GM Side, "L", Stud, combination SAE and Stud, and combination SAE Post and GM Side. For automotive applications, the SAE Post is the most popular, followed by GM Side, then the combination "dual" SAE Post and GM Side. "L" terminal is used on some European cars, motorcycles, lawn and garden equipment, snowmobiles, and other light duty vehicles. Stud terminals are used on heavy duty and deep cycle batteries. The POSITIVE (+) SAE terminal post is slightly larger, 1/16 inch (1.6 mm), than the NEGATIVE (-) post. Terminal types, locations and polarity will vary. There are adapters available that will you allow to connect cables with "GM" style side terminals to batteries with top post terminals or visa versa.

[Source: BCI]

Battery manufacturers or distributors will often "private label" their batteries for car manufacturers, large chain stores or export. An alphabetical list of most of the largest battery manufacturers/distributors, their Web addresses, telephone numbers and some of their brand names, trademarks and private labels can found in the Battery Manufacturers & Private Labels List at http://www.batteryfaq.org/. Ownership, branding, Web addresses and telephone numbers will sometimes change.

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7.6. Freshness

Lead-acid batteries are perishable and sulfate in storage due to their natural self discharge.

Determining the "freshness" of a battery is sometimes difficult. Unless it has been periodically recharged or "dry charged", NEVER buy a wet Standard (Sb/Sb) or Low Maintenance (Sb/Ca) battery that is MORE than three months old or a wet Maintenance Free (Ca/Ca) battery that is MORE than six months old. Dry charged batteries are shipped without electrolyte, but usually have "sell by" dates of one to three years. Depending on the temperature, AGM and Gel Cell batteries that can be stored six to 18 months before the State-of-Charge drops below 80%. Please see Section 16. for more information on sulfation. Dealers will place their older batteries in storage racks so they will sell first and they do not have to maintain them. The fresher batteries can be found in the rear of the battery rack or in a storage room. For a wet battery, the date of formation is often stamped on the case or printed on a sticker. Always have a new battery tested, and recharged if necessary, before you leave the store. This can save you a lot of time and frustration if the new battery is sulfated or has a manufacturing defect.

Some of the manufacturer's formation date coding techniques are as follows:

7.6.1. Delphi (ACDelco) and some Sears DieHard

Dates are stamped on the cover near one post. The first number is the year. The second character is the month A-M, skipping I. The last two characters indicate geographic areas. For example, 0BN3=2000 February.

[Source: Interstate Batteries]

7.6.2. Douglas

Douglas uses the letters of their name to indicate the year of manufacture and the digits 1-12 for the month. D=1994 O=1995 U=1996 G=1997 L=1998 A=1999 S=2000 For example, S02=2000 Feb.

7.6.3. East Penn, Exide (Champion), Johnson Controls Inc., Interstate, Mopar (Chrysler) and some Sears DieHard)

Usually on a sticker or hot-stamped on the side of the case. A=January, B=February, and the letter I is skipped. The number next to the letter is the year of shipment. For example, B0=Feb 2000.

        

[Source: Interstate Batteries]

7.6.4. Exide (some Sears non-Gold DieHards)

The fourth or fifth character is the month. The following numeric character is the year. A-M skipping I. For example, RO8B0B=February 2000.

[Source: Interstate Batteries]

7.6.5. Optima

The first character is the year. The following three numeric characters are the days of the year. For example, 3123=3 May 2003.

7.6.6. Trojan

The date code on the negative post is stamped as the battery comes off of the finishing line, ready to ship out or go into stock. The code that is stamped is usually one month ahead. Therefore, a battery that comes out in March will carry an April date code. The code on the positive post is the manufacturing date that indicates when the battery was physically built but before the addition of any electrolyte. The letter is the month (A=Jan, B=Feb, C=March, etc.) and the number is the actual date. So "K26" means that the battery was ready for electrolyte filling and the first forming charge was on November 26th. Since the negative post shows A2 (January 2002), the manufacturing year has to be 2001.

7.6.7. Concorde

The activation date is on an orange sticker the shipping carton or email Concorde Customer Service with the serial number of the battery.

7.6.8. Rolls and Surrette

The four digit date code represents the day of the week (first digit), week of the year (middle two digits) and the year (last digit). For example, April 4, 2003 would have 4143 as a date code. The date code is stamped into the front edge of the cover of the battery.

If you cannot determine the date code, ask the dealer or contact the manufacturer. Because of permanent sulfation, fresher is definitely better and does matter.

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7.7. Warranty

Battery warranties are not necessarily indicative of the quality or service life. Some dealers will prorate warranties based on the list price of the bad battery, so if a battery failed half way or more through its warranty period, buying a new battery outright might cost you less than paying the difference under a pro rated warranty. The exception to this are the free replacement warranties. They represent the risk that the manufacturer is willing to assume. A longer free replacement warranty period is better.

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7.8. Buying Tips

The following are some tips for consumers for buying car, motorcycle, truck, marine and recreational vehicle starting and deep cycle batteries. Before you buy a replacement battery, you should fully charge your old battery, remove the surface charge and test it. You could have a faulty charging system.

7.8.1. Size matters!

Purchasing a battery has become much easier because most of the battery and vehicle manufacturers have adopted the BCI Group Number, ETN or JIS as a standard for the battery's voltage, physical size, terminal type and terminal location. Web based Battery Selectors published by battery manufacturers or distributors can make the task even easier. They contain the vehicle's minimum cold cranking amps (CCA) requirement and battery size replacement recommendations by make, model and year of manufacturer.

7.8.2. Pick the battery type that matches your charging system.

For starting an engine, using a car battery is normally a better choice than a deep cycle battery because it is specifically designed for shallow (1%-3%) discharges. The battery type MUST match your vehicle's charging system or you could damage the new battery or charging system. The easiest way to accomplish this is to replace your battery with the same or compatible type of battery that was originally installed by the vehicle's manufacturer. The exception to this is in hot climates, using a non-sealed wet car battery (with filler caps) is highly encouraged because lost water can be easily replaced. For batteries with side terminals commonly found in General Motors vehicles, check the terminal bolt length and do not over tighten because you might crack the battery case and cause a leak.

For a deep cycle application, using a deep cycle battery is much better alternative than using a car battery.

7.8.3. For car batteries, select the battery with CCA (Cold Cranking Amps) that will meet or exceed the vehicle manufacturer's recommendation.

Do not substitute CA (Cranking Performance Amps), MCA (Marine Cranking Amps), or HCA (Hot Cranking Amps) for CCA. In hot climates, buying batteries with double or triple the cranking amps that exceeds your starting requirement is a waste of money. However, in cold climates, higher CCA ratings are better, due to increased power required to crank a sluggish engine and the inefficiency of a cold battery.

7.8.4. More Reserve Capacity (RC) or Amp Hours (AH) is a good thing.

Greater RC or AH is better because of the effects of increased parasitic (ignition key off) loads, normal battery self discharge while the vehicle is not being used or in storage, and the demands of stop-and-go driving. Amp Hour (AH) ratings are normally used to describe the capacity of deep cycle and European car (starting) batteries. When comparing AH specifications, use the same discharge rates, expressed in hours. The most common is the 20 hour rate which is expressed as "C/20". A heavier battery has more lead and is normally better choice.

Batteries are generally sold by model or series, so the battery sizes can vary for the same price. This means that for the same price, you can potentially buy a larger battery with more RC or AH than the battery you are replacing. If you buy a physically larger battery, be sure that the replacement battery will fit, the cables will connect to the correct terminals, and that the terminals will NOT touch metal surfaces such as a closed hood (or bonnet).

7.8.5. Batteries are perishable, so buy the FRESHEST available.

Unless a battery has been periodically recharged, never buy a non-sealed wet Standard (Sb/Sb) or Low Maintenance (Sb/Ca) battery that is more than three months old, a sealed wet Maintenance Free (Ca/Ca) battery that is more than six months old, or sealed AGM or Gel Cell battery that is over 12 months old, because it has started to sulfate. "Dry charged" batteries are shipped without electrolyte and usually have "sell by" dates of one to three years. Battery dealers will often place their fresher batteries in the rear of the battery rack or in a storage room. The date of manufacture is often stamped on the case or printed on a sticker. Always have a new battery tested, and recharged if necessary, before you leave the store.

7.8.6. Look for longer free replacement warranties.

Pro rated battery replacement warranties are not necessarily indicative of the quality or cost over the life of the battery. The exception is the free replacement warranty, which represents the risk that the manufacturer is willing to assume.

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7.9. How Do I Size For Backup AC Power?

For backup power, here are the steps for sizing the battery bank, inverter, AC battery bank charger and generator based on your AC power requirements. Battery bank capacity sizing is based on power requirements, inverter efficiency, wiring power loss, discharge rate (Peukert Effect), electrolyte temperature, and desired average Depth-of-Discharge. DC AC Power Inverters has a simple and easy to use battery capacity calculator at http://www.dcacpowerinverters.com/faq.htm#22.

7.9.1. Calculate the cumulative daily AC load in amps hours (AH) at 120 VAC. This will require determining how much current an appliance uses and for how long times the "duty cycle" (the amount of time the appliance is on during that time period).

For example if you have:

a. Two 60 watt lights that you use continuously for four hours, the calculation would be 60 watts/120 volts x 4 hours x 2 lights = 4 AH.

b. A 200 watt refrigerator that is on for 24 hours with a 25% duty cycle, the calculation would be 200 watts/120 volts x 24 hours x 25% = 10 AH.

c. A five amp power drill that you use 15 seconds at a time for 25 times, the calculation would be 5 amps x 15 seconds / 60 seconds / 60 minutes x 25 = .52 AH.

c. A 10 amp sump pump that is on 24 hours and has a 50% duty cycle, the calculation would be 10 amps x 24 hours x 50% = 120 AH.

The daily sum of these four appliances would be 4 AH + 10 AH + .5 AH + 120 AH = 134.5 AH at 120 VAC.

7.9.2. Depending on the efficiency of the inverter and the power loss in the wiring, it takes between 12 and 14 amps of 12 VDC power to produce one amp of 120 VAC power or 24 to 28 amps to produce one amp of 240 VAC. Using the above example in the worst case, it will require 14 x 134.5 AH = 1883.3 AH per day.

7.9.3. Depending on the average load on the battery bank, the capacity may have to be adjusted due to the Peukert Effect that basically says that the higher the discharge rate, more capacity is require to produce the same amount of power. 12-volt deep cycle batteries are normally rated by the fully charged capacity divided by the number of hours of discharge it take to drop to 10.5 VDC. A very common rate is over a 20 hour period and is is expressed as "C/20". In the example above, 1883.3 AH are being consumed in a 24 hour period which has a slightly lower rate that over a twenty hour period, so we could probably derate the daily capacity by 10% or 1883.3 AH x .9 = 1695 AH per day. If all of this power were consumed over six hour period, you would probably need to increase the daily battery capacity by approximately 25%.

7.9.4. Depending on the temperature of the battery electrolyte, the capacity might also have to adjusted. The example above assumes 80 degrees F. If your battery bank was operating at 60 degrees F then you would have to increase the capacity by 10% and at 32 degrees F, by 20%. Let's assume the batteries are in a heated area at 70 degrees, so you would increase the daily capacity by 5% or 1695 AH x 1.05 = 1780 AH per day.

7.9.5. Depending how many discharge/charge cycles you want your battery bank to last, you will need to increase the capacity. Let's assume that you are using "low end" inexpensive deep cycle batteries that at 0% average Depth-of-Discharge (DoD) will last 50 cycles, at 20% average DoD will last 200 cycles and at 50% average DoD will last 500 cycles. In the example, for 0% average DoD, you would require a battery bank with a daily capacity of 1780 AH, at 80% DoD (1780 AH / 80% = 2225 AH), and at 50% DoD (1780 AH / 50% = 3560 AH).

7.9.6. Once you have determined your daily capacity, then you need to determine how many hours or days you want to run using your battery bank before you recharge your batteries.

7.9.7. To size the inverter using the example above, calculate the worst case load (with all the appliance on at once) which is (60 watts x 2 lights) +200 watts + (5 amps x 120 volts) + (10 amps x 120 volts) = 2120 watts @ 120 VAC. You will need to consider the start surge power requirement of up to five time the run current with large inductive starting loads, such as motors and transformers.

7.9.8. To size the battery charger, you will what the output to be at least 10% of the battery capacity to fully recharge the batteries within 24 hours. Using the example above, you would need a 175 amp charger at 0% DoD, 225 amp at 20% DoD, and 350 amps at 50% DoD.

7.9.9. To size an AC generator, using the example above without recharging the battery bank, the worst case load (with all the appliance on at the same time) is (60 watts x 2 lights) + 200 watts + (5 amps x 120 volts) + (10 amps x 120 volts) = 2120 watts @ 120 VAC. You would also need to consider the surge power requirement up to five times the run load. If you are using motors, take into consideration their peak starting current. If you want to recharge the batteries in addition to using your appliances, you would need to add 2800 watts for 0% DoD, 3500 watts for 20% DoD, and 5500 watts for 50% DoD to power the battery charger.

As you can see from this example, using just battery backup for one day for AC power with a heavy load can become very expensive, so that is why most "grid" power backup systems is an AC generator, combination of batteries and AC generator, or combination of battery and solar power with AC generator backup.

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