Question: How does a battery recharge? What is happening inside? Answer: a. The chemical actions that take place within a battery during charge are basically the reverse of those that occur during discharge. When a battery is charged, the sulfate (PbS04) in both plates is split into its original form of lead (Pb) and sulfate (S04). The water is split into hydrogen (H) and oxygen (0). As the sulfate leaves the plates, 'it combines with the hydrogen and is restored to sulfuric acid (H2S04). At the same time, the oxygen combines chemically with the lead of the positive plate to form lead dioxide (Pb02). The specific gravity of the electrolyte increases during charge because sulfuric acid is being formed and is replacing water in the electrolyte. Any lead acid battery will evolve gas while it is being charged. Hydrogen is given off at the negative plate and oxygen at the positive. These gases result from the decomposition of water (H20). Abattery gasses (and uses water) because it is being charged at a higher rate than it can accept. This may be due to the fact that the battery is fully charged, that its plates are sulfated, or that it is too cold to accept a charge. A battery will gas near the end of a charge because the charge rate is too high for the battery to accept all of it. A temperature compensating, voltage regulating charger which automatically reduces the charge rate as the battery approaches the fully charged state eliminates most of this gassing, it is extremely important not to charge batteries for long periods of time at rates which cause them to gas because this means they are using water which, in sealed batteries, cannot be replaced. Of course, no battery should be overcharged for a long period of time. b. The relationship between specific gravity readings and the combination of the sulfate from the acid with the positive and negative plates at various states of charge: A fully charged battery has all of the sulfate in the acid. As the battery discharges, some of the sulfate begins to appear on the plates. The acid becomes more dilute and its specific gravity drops as water replaces more of the sulfuric acid. A fully discharged battery has more sulfate in the plates than in the electrolyte.