One of the most important properties of lead–acid batteries is the capacity or the amount of energy stored in a battery (Ah). This is an important property for batteries used in stationary applications, for example, in photovoltaic systems as well as for automotive applications as the main power supply.
Lead–acid batteries exist in a large variety of designs and sizes. There are vented or valve regulated batteries. Products are ranging from small sealed batteries with about 5 Ah (e.g., used for motor cycles) to large vented industrial battery systems for traction purposes with up to 500 Ah.
Sealed lead–acid batteries are constructed differently and have hydrogen and oxygen gases recombined inside a cell. While the majority of lead–acid batteries used to be flooded type, with plates immersed in the electrolyte, there are now several different versions of lead–acid batteries.
Lead–acid batteries are the dominant market for lead. The Advanced Lead–Acid Battery Consortium (ALABC) has been working on the development and promotion of lead-based batteries for sustainable markets such as hybrid electric vehicles (HEV), start–stop automotive systems and grid-scale energy storage applications.
Normally, as the lead–acid batteries discharge, lead sulfate crystals are formed on the plates. Then during charging, a reversed electrochemical reaction takes place to decompose lead sulfate back to lead on the negative electrode and lead oxide on the positive electrode.
The battery may also fail as an open circuit (that is, there may be a gradual increase in the internal series resistance), and any batteries connected in series with this battery will also be affected. Freezing the battery, depending on the type of lead acid battery used, may also cause irreversible failure of the battery.