Lead acid batteries are classified as a secondary battery. Secondary batteries are all types of batteries that can be reused because you can recharge it. There are around 13 types of secondary batteries on the market today. Our concern here is only with the lead acid battery. The known problem with lead acid batteries is that after a certain period of usage the battery decays to a state where accepting and holding a charge is no longer possible. Everyone that owns a motor-vehicle like a car or truck knows about this phenomenon. Owners of motor-vehicles often are surprised to find that their battery is not rendering the power it should after a session of charge and this failure manifests prior to the end of the expected warranty term provided by the battery manufacturer.
Lead acid batteries vary according to the electrolyte. Some lead acid batteries are made using a gelatinized electrolyte, hence the name of Gel battery. However, most batteries are made with a liquid electrolyte made of sulfuric acid. The issue with premature failure of batteries include various aggravating factors such as the high procurement cost of replacement, the cost of business daily operation interruption due to down time, damages that can occur to the electric and electronic system in the forklift or in a backup power supply unit.
Once a battery fails to accept a charge and fulfil its work capability, the battery is discarded or considered spent or scrap. Two questions that rise from this reality are: Why does this happen? What can be done to reduce battery failure? All lead acid batteries, flooded and Gel, sealed or vented, of any brand name and size must sustain this cycle of charge and discharge of both plates in each cell to keep forming soft lead sulphates at least until completing its warranty life. Even if the battery fails to reach the desire state of charge as per manufacturer specifications before or after life warranty, the fact is that all batteries that fail to be charged again do so because the plates (electrodes) in each cell pack remain discharged or depolarized. If an electrode (plate) remains discharged or do not reach at least 80% state of charge it is because a portion of the electrode, after a cycle of charge, has remained with the lead sulphates (PbSO4) that did not decompose back to the original ingredients. This lead sulphates have become too hard to disassemble using regular or standardized battery charging equipment.
The first question, “Why does this happen?”, has an easy response:
lead acid battery failure is due to a hardening of lead sulphate on the electrodes or plates in each cell pack. From an electrochemical point of view, when charged, all forklift batteries have cells that contain two electrodes of which one is negatively charged made of lead (Pb) and the other is positively charged made of lead dioxide (PbO2). These electrodes of oppose polarities are submerged in an electrolyte of approximately 33.5% sulfuric acid (H2SO4) and 63.5% water (H2O). When a charged battery is used or under a load that discharges the battery, both electrodes go through an electrochemical reaction that turns the Pb in the negative plate, the PbO2 on the positive plate, and the H2SO4 in the electrolyte into lead sulphate (PbSO4). Due to this chemical reaction, the electrolyte loses the dissolved sulfuric acid and becomes mostly water. Thus, when a lead acid battery is discharged lead sulphates (PbSO4) are formed on both plates and when charged again the lead sulphates decomposes back to original active materials of PB, PbO2, H2SO4, and H2O.