Lead-acid batteries are relatively simple electrochemical devices able to store electrical energy and deliver it to motors and other appliances when needed. Unlike common dry cell or alkaline batteries used in torches and other household appliances, lead-acid batteries may be recharged after the stored energy has been used. This is why they are widely used in starting motor vehicles and running appliances (e.g. air conditioning, headlights). Although the starter motor and headlights use much of the battery’s stored energy, the battery is continuously recharged by the alternator during the normal running of the engine. 

 

Lead-acid batteries are made up of sheets of lead immersed in a ‘bath’ of sulfuric acid. Usually, the whole assembly is contained in a robust plastic case made of polypropylene or polyethylene. Although lead-acid batteries may be charged and re-charged many times, each cycle places small stresses on the lead plates, which eventually distort. This causes short circuits within the battery so that the battery is unable to hold stored energy for a prolonged period. Depending on operating conditions and other factors, a number of other processes may take place in the battery which coats the plates with scale or other non-reactive material, making them difficult or impossible to recharge.

As a result of these degradation processes, batteries become unusable and are then known as used lead-acid batteries (ULABs) and are waste. In Australia, the lifetime for motorcar batteries is typically three to four years, while for trucks and tractors the typical lifetime is two to three years.