Most car's alternators run the electrical system at about 14 volts, and then when the car is shut off, the fully charged battery should read about 12.8 volts. Unless your alternator is not working, it should not be running a 12.8 while the car is running, unless you have a big electrical load i.e. heated seats, rear defogger, heated mirrors. However, I doubt if your alternator is not working, because you would probably have a dead battery by now.rickbb63 said: