Automotive electrical question?

Battery testers do not test alternator voltage output. For that you need an inexpensive volt (multi-tester.) With the engine running you should see between 13.5 - 14.0 volts. Volt meters also can be used to check battery voltage with the motor off. It's best to check battery voltage after the car has been at rest cold over night. A fully charged battery should test 12.85 volts. If not, charge @ 2 amps with an automatic self leveling battery charger. Have a *load test done on your battery and check both ends of both battery terms to make sure they are clean dry and tight.