Old battery of abotu 8 years died. I replaced it. Two weeks later, my new battery is dead. The car will jump start, and run fine, but as soon as the car is turned off it won't restart, even with 20-30 mintes of run time. with all accessories on, engine running the voltage at the battery terminals is 14.7 volts. Turned off, engine off, the battery read 9 volts. Se my new battery junk or could the voltage regulator be bad and cooked both batteries? I need to have a working car so please help.