Battery Glossary

Lead Acid Batteries

Lead Acid Batteries are the oldest form of rechargeable battery. Rechargeable batteries are also referred to as 'secondary batteries'.

This type of battery is notable in that it contains a liquid in an unsealed container, requiring that the battery be kept upright and the area be well ventilated to ensure safe dispersal of the hydrogen gas produced by these batteries during overcharging.

Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large power-to-weight ratio. These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by automotive starter motors.

Read more about the difference between car batteries & deep cycle batteries.

License: Some of the information on this page was gathered from Wikipedia and is therefore released under CC-BY-SA License.

Wet Cell or Flooded Batteries

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wet or flooded cell battery operates by means of a liquid electrolyte solution (battery acid) covering all internal parts. Wet-cell batteries produce gas when overcharging. This gas must be able to escape which is why some refer to this type of battery as vented cell battery. Some types of wet batteries claim to be 'sealed'. These are VRLA batteries (see below).

Wet cells are still widely used in cars, stationary (large) uninterrupted power supplies and of course, stand alone energy systems.

Dry Cell or Sealed Batteries

Dry cell or sealed batteries comprise the majority of batteries used in the home and are found in many household items including torches, toys, radios, cameras, power tools, mobile phones and laptop computers.

'Dry Cell' is an antonym to wet cell batteries. Rainbow Power Company refrains from using the term 'dry cell' as it could be misleading. Firstly, dry cell batteries are not as dry as the name suggests: they contain moisture in a paste or mat. Secondly, wet batteries are usually delivered without acid which literally makes them dry. (Caution: Using wet batteries in a 'dry' state will result in 'dead' batteries)

'Sealed' is also slightly misleading, as no lead acid battery is truly sealed. In most situations a sealed battery recombines the oxygen produced at the positive plates with the hydrogen from the negative plates. However, a battery can create excessive pressure which must be released to prevent explosion.

We therefore prefer the term 'valve-regulated lead-acid battery' (VRLA). See next section.

Valve-Regulated Lead-Acid Batteries

A valve-regulated lead-acid battery (or VRLA battery) is an improved type of liquid electrolyte battery. Because of their construction, VRLA batteries do not require regular addition of water to the cells and are commonly advertised as 'no maintenance' batteries. VRLA batteries are further classified as:

  • Absorbed Glass Mat (AGM) batteries
  • Gel batteries

These batteries are often referred to as sealed lead-acid batteries, but they always include a safety pressure relief valve. As opposed to wet (also called flooded) batteries, a VRLA cannot spill its electrolyte if it is inverted. Because AGM VRLA batteries use much less electrolyte (battery acid) than traditional lead-acid batteries, they are also occasionally referred to as an "acid-starved" design.

Absorbed Glass Mat Batteries

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Absorbed glass mat (AGM) batteries were originally developed for the military as a temperature tolerant and vibration resistant power source. These batteries hold the electrolyte on the glass mat separator.

Some advantages over wet cell batteries:

  • no spilling of acid
  • low maintenance (no top up needed)
  • temperature tolerant (operate at -20°C)
  • vibration resistant
  • they can be (occasionally !) discharged much deeper without major damage
  • they can be charged much faster

Gel Batteries

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A gel battery (also known as a "gel cell") is a VRLA battery with a 'gelified' electrolyte. Unlike a flooded wet-cell lead-acid battery, these batteries do not need to be kept upright. Gel batteries reduce the electrolyte evaporation, spillage (and subsequent corrosion issues) common to the wet-cell battery, and boast greater resistance to extreme temperatures, shock, and vibration. Chemically they are the same as wet (non-sealed) batteries except that the antimony in the lead plates is replaced by calcium.

Lithium Batteries

Lithium batteries are actually single-use, non-rechargeable batteries (or "primary" batteries), found in small devices like calculators or timers, and known for their long service life. They are also referred to as lithium-metal batteries. RPC does not sell any lithium-metal batteries, or primary batteries for that matter. The term "Lithium Batteries" is, however, also sometimes (incorrectly) used as heading for the various chemistries of rechargeable Lithium-ion batteries.

Lithium-ion Batteries

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Lithium-ion batteries, or Li-ion for short, are rechargeable batteries with a very high energy density. This results in smaller and lighter batteries when compared with other battery technologies or chemistries. They also have a very low self discharge rate, which means they have a long shelf life; in fact, Lithium-ion batteries will stay nearly fully charged even after many weeks of storage. Biggest advantage is the high charge and discharge capacity. Lithium-ion batteries can deliver up to 100% of their nominal capacity.

There are a number of types of Lithium-ion batteries, with different chemistry and other characteristics. RPC recommends Lithium Iron Phosphate for off-grid solar systems.

Lithium Iron Phosphate Batteries (LiFePO4 Batteries)

Lithium Iron Phosphate, or LiFePO4 Batteries, are a type of Lithium-ion battery with an energy density that is slightly lower than that of other Li-ion chemistries (e.g. LiCoO2) as they have a lower operating voltage. However, due to their Iron Phosphate cathode chemistry, LiFePO4 batteries are practically incombustible - even when rapidly charged or discharged. This safety aspect gives Lithium Iron Phosphate the edge over other chemistries, as spikes of high currents are common in households. In addition, LiFePO4 can deliver higher peak currents than other Li-ion batteries.