BatteriesBATTERY THEORYAs a lead-acid battery is charged in the reverse direction, the action described in the dischargeis reversed. The lead sulphate (PbSO4) is driven out and back into the electrolyte (H2SO4). Thereturn of acid to the electrolyte will reduce the sulphate in the plates and increase the specificgravity. This will continue to happen until all of the acid is driven from the plates and back intothe electrolyte, as shown in Equation (4-2) and Figure 5.Figure 5 Chemical Action During Charging(4-2)PbO2Pb2H2SO4charge2PbSO42H2OAs a lead-acid battery charge nears completion, hydrogen (H2) gas is liberated at the negativeplate, and oxygen (O2) gas is liberated at the positive plate. This action occurs since the chargingcurrent is usually greater than the current necessary to reduce the remaining amount of leadsulfate on the plates. The excess current ionizes the water (H2O) in the electrolyte. Sincehydrogen is highly explosive, it is necessary to provide adequate ventilation to the batterywhenever charging is in progress. Also, no smoking, electric sparks, or open flames are allowednear a charging battery.Rev. 0 Page 7 ES-04
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