To rebuild a car battery, you need to first start by testing the battery for charge capacity. You also need to check the acid ratio and then you drain the acid from the case of the battery. The next step is to refresh the acid and replace the caps on it. You then charge the battery for 24hours to get it to full charge. You can get the step by step process at http://www.ehow.com/how_5244691_rebuild-car-battery.html.