On a 97 cad.deville northstar the car will sit up two or three days when I try to start it up it just drag and click, so I unhook the battery cables and charge the battery up to 13.0, and I let the sit up with the cables unhook over night and half of the day. The battery had discharge down to12-5 what going on is 12-5 volt enought to crank the car, are the battery bad or what.What is the right charge for a good battery