A 12V Lead Acid battery has many uses, both in small and large applications. With this type of battery, it is critical to understand its capacity – which is measured in Amp-hours (Ah) or Milliamp-hours (mAh). This is the amount of energy output from the battery before requiring a recharge.
This comes to 167 watt-hours per kilogram of reactants, but in practice, a lead–acid cell gives only 30–40 watt-hours per kilogram of battery, due to the mass of the water and other constituent parts. In the fully-charged state, the negative plate consists of lead, and the positive plate is lead dioxide.
One of the most important factors to consider when buying and using a 12V lead acid battery is its capacity. In general, these batteries have a much longer lifespan than other types. But must still be regularly maintained in order to truly benefit from their longevity.
A typical lead–acid battery contains a mixture with varying concentrations of water and acid. Sulfuric acid has a higher density than water, which causes the acid formed at the plates during charging to flow downward and collect at the bottom of the battery.
In 1992 about 3 million tons of lead were used in the manufacture of batteries. Wet cell stand-by (stationary) batteries designed for deep discharge are commonly used in large backup power supplies for telephone and computer centres, grid energy storage, and off-grid household electric power systems.
The capacity of a lead–acid battery is not a fixed quantity but varies according to how quickly it is discharged. The empirical relationship between discharge rate and capacity is known as Peukert's law.