A discharging lead acid battery is best described as

Lead acid battery is the oldest type of rechargeable battery. The battery in constructed of several single cells connected in series. Lead acid batteries do not generate voltage on their own. They only store a charge from another source.

The battery must first receive a (forming) charge voltage of at least 2.1-volts/cell from a charger. The size of the battery defines the amount of charge the battery can store.