So I had the brake and battery light come on, I got my alternator and battery checked at auto zone and they said both of them were fine. The light kept coming on so I changed the battery. I thought it was fine when later that day I started it and the lights on the dash were on longer than usual. So now I’m assuming it’s the alternator that is the problem. Running voltage for the battery was 13.24, resting voltage was 12.6. Is there anything else to test or is the alternator 100% at fault?

 

It’s probably the alternator. I had this happen on my old maxima. The light would come on then go off, and each time seemed to stay on longer. Eventually it died at a stop light, and I caused a half mile of traffic on an arterial road from 4-6pm on a Thursday…. So yeah.

 

Disconnect the battery and fully check/clean all connections at the alternator. Make sure the battery posts are clean and reconnect. If the BATTERY/ BRAKE lights keeps turning ON, then you need to get the alternator properly checked. Only a proper bench test, with specific equipment, can determine if the alternator is good, no good, or dying. Do you drive at night and, if so, do you notice any slight flickering of your lights (interior and exterior)?

No offense to any of those parts stores, but their handheld gadget is not adequate, IMO, to fully test a alternator.