Hi guys. My 1 year old battery died a few times in last month and happened again today. So, I went to Autozone to get the battery tested and they said it's fine but since it's only 1 year old they gave me new one.

So I tested my charging system according to the instruction in FAQ and I got some different numbers than good and bad at certain cases. Here are the results.

1) Engine off - 12.3 V (New Battery)
2) Engine on and idle - 13.5 V constant
3) Engine on and only AC, radio, wipers, blinkers on - 13.39 V - 13.45 V
4) Engine on and everything on (headlights, AC, radio, Wipers, etc) - 12.99 V constant

It doesn't change at all when I rev it to 3k RPM except in case 3. It drops the voltage to 13.39 V instead. Autozone told me that it's not their battery problem but my car's problem. Is my alternator becoming weak?

 

The first two are in spot 13.5v is the less you want to see.

But 12.99v @ 3k isn't good. Take the alternator to test looks like it's start to give up.

 

Charging voltage with no load should be around 14v -14.5v. Definitely sounds like an alternator issue.

Take it off. They can also test that for free at Autozone. It just needs to be off the car to do so.

 

New results.

1) Engine off - 12.3 V (New Battery)
2) Engine on and idle - 14.11 V constant
3) Engine on and only AC, radio, wipers, blinkers on - 14 V - 14.10 V
4) Engine on and everything on (headlights, AC, radio, Wipers, etc) - 13.66 V constant

This time, when I rev to 3000 RPM, it raises the voltage except when all loads are on. All I did was took the alternator out, open it up and cleaned it and resoldered it. I am not sure it's a good idea for a long run. I also readjusted the tension of belt based on factory specs. Any suggestions?

 

around 13v with a load then it sounds like the alternator brushes are worn or the regulator is going out

if the headlights slowly dim with the car running then the alternator diode isnt converting the voltage to DC.