It sounds like alternator time and specially if you are reading only 12 volts. To be accurate you should use a digital volt meter. A fully charged battery reads 12.6 volts. With the engine running, you should measure at least 13.2 volts across the battery which is alt output. If you are reading 12 volts, the alt isn't working and the battery is dead.

Peter

__________________
Auto Zentral Ltd.