Sister in law had a dead battery in her car. Would jump start the car and show charging, but wouldn't hold a charge after the car shut off. Battery test under load was not good. Can't recall exact numbers, but was junk. I have a Battery Minder 1510 that I tried to use to desulfate on. Battery was too weak for it to work. I charged the battery with a standard charger and got the voltage up, but would slip over night. I put the battery on the charger and when it hit enough volts per the Battery Minder manual (10.5V), I hooked that up and let it do it's thing. After a few days on it, I pulled the Minder off and let it sit for a few days. Seemed to hold a charge around 12 Volts. We put in a new battery anyway, but used the dead one to experiment with.