Take the battery to any store that sells new ones other than Auto Zone. Ask for a free 15 second battery load test to see what the reserve amperage capacity is. Amperage spins starter motors not voltage.
From now-on never buy your replacement electrical parts from Auto Zone.
The 14-15 volts means that the alternator is working.
1 What make and year truck?
2 Did you test the battery?
2a Did you load test the battery?
3 What is the battery voltage with the vehicle off and nothing on?
4 Are there any issues with the vehicle cranking?
5 Did you check ALL fuses and circuit breakers for continuity?
6 If you are able to get to the battery connections safely while the engine is running at idle, can you disconnect the Negative cable from the battery? If you can disconnect it while the engine is running and have ALL accessories OFF, the engine will die if the alternator is no good. On the contrary, the engine will continue to run at idle using the alternator as its source of electrical power. Just do this for a 10 seconds or less and shut the key off.. You can reconnect the Negative cable.
Well if you replaced the alternator and the problem is still persisting, I think you have your answer. It doesn't matter if the car is stopped. As long as the engine is running, the belt is driving the alternator which is generating electricity. While idling, your battery should have a current reading of 13.5 or higher. If not, the alternator isn't doing it job. Conversely, the battery should have a charge no lower than 12.4 with the engine is off.
When I first start the truck up, I get a battery indicator light and the volt meter reads about 9V. It slowly goes back up to between 14-15V but the indicator stays on.
If I have to stop at a red light, the battery voltage starts dropping back down to around 9V. The moment I start moving again, the voltage JUMPS back to 14-15V.
I did a little experiment while stopped at a red light. I placed the truck into park to see what the battery (or alternator) would do. To my surprise, the voltage started going back up...
I replaced the alternator with a new one about 3 months ago and everything was fine until last week.
If the battery was losing its charge while driving I would definitely say the alternator. This has me slightly confused because it appears the alternator is doing it's job as long as the car is driving but not when it is stopped.
