How The Battery Works: Charging
Applying voltage to the battery from an external source such as the generator or battery charger reverses the chemical action in the battery.
Reversing the chemical action in the battery, forces the free electrons at the negative terminal of the battery back into the electrolyte raising the sulfuric acid percentage. This chemical action removes the Lead sulfate that had formed on the negative plates leaving pure active material.
The electrons that were forced into the electrolyte are able to react with the lead sulfate on the positive terminal again raising the Sulfuric acid content and leaving pure active material on the positive plates.
This process enables the battery to be used over and over again.