My battery went bad, had a dead cell so I bought a new Duralast Gold battery at Autozone yesterday. After driving home 25 miles, the battery has 12.67 volts with the engine off and 13.6 volts with the engine running and no lights or AC on. When I have the engine idling and the AC, bright lights and stereo on, it still has 13.6 volts at the battery terminals.

The way I learned it is with the engine running you should have at least 14 volts at the battery with the engine running, anything less means the alternator is either weak or not working at all. I have also read that a weak battery will make an alternator work too hard and damage the battery and a weak alternator will damage a good battery too.

Anybody else have info on this? What kind of voltage do you guys have on your battery/alternator? My truck runs fine but I will buy a new alternator if I need to. The alternator on my truck is the original, 135,000 miles on it and it's 10 years old.

Thanks.

Jimmy

 

I've always thought as long as you were getting 13.5 to 14 volts it was fine anything under means alt is going or it has bad connections. You could always take off and have autozone test it.

 

13.6 is about right. You should have 14.0 or more at 1500-2000 RPM.

 

I thought so too, it just seems to me that 13.6 volts is at the very low end of acceptable voltage. I will get it tested just to be sure it's OK. The alternator on my gf's 4cylinder Honda Accord has 14.25 volts at the battery with the engine ildling and 14.10 with the engine idling and the AC and bright lights on. That's what brought this up.

Coincidentally, her battery failed yesterday too. She had trouble starting her car day before yesterday, it started but she didn't tell me about it until yesterday when her battery was dead at her work. So I had to get a new battery for my truck then go to her work, jump start her car and go to Autozone and she bought a Duralast Gold for her car too, and I put her battery in in the Autozone parking lot.

That's what started me checking all the voltage on both her car and my truck. Seems to me I should have 14-point-some-odd volts too. I guess Autozone can test the alternator better than I can with just a volt meter.

Thanks.

Jimmy

 

Autozone tested the battery and alternator for me after work today. They used a hand-held load tester but it still had the same 13.6 volts and the tester said the alternator and its internals were all OK. I am going to leave well enough alone on the alternator but tomorrow I am going to remove and clean the grounds on the frame and at the engine block and clean all the connections on the back of the alternator, just so I know I have good grounds and power connections for it and the rest of the truck too. It might increase the alternator output but I won't worry if it doesn't.

I also realized that the reason why my gf's Honda has more voltage at the battery may be because she just has a higher output alternator than I do. Her car is much more electonically sophisticated than my plain old pickup truck and hers has a lot more electronic accessories than my truck does, plus an automatic tranny that is probably electronically controlled too. And Honda's have those puny little lawnmower sized batteries so it probably needs a more powerful alternator to keep everything charged up and running.

Thanks for the help here.

Jimmy

 

I know my old dually had 12.5 sitting, 13.2 idling and 13.8 running. But it was an umpteed year old who-knows-what-store special.

We have an east cost electric on our camaro with two optima red's, it's around 11.5 volts sitting, 12.5 volts idling, and 15 volts at 6000+ RPM.