lrogers0613

Hey guys my battery light has been coming on randomly. In the mornings it'll come on after driving for about 2 minutes then it'll go off in like 10 minutes. Usually it won't come on again the rest of the day. Almost always comes on once and then stays off. Not sure what is happening. I've teated battery when the car isn't running and it is 12.7. BTW the battery is 2 months old, because my last one went out. Also tested the alternator and it was charging at 14.45. All those numbers seem good to me so not sure what's going on. Any help is appreciated.

Lethaldosage423

you need to do a load test on the battery. apply cranking voltage to it and see what the battery drops to. anything under 9 volts is unacceptable. also its good to do this a few times because sometimes a battery can hold great for 10 seconds and then drop voltage.

I'm pretty confident that you have a failing diode in your alternator. I would have someone crank the car over while you check the voltage. after cranking, once the car starts running, the voltage should immediately spike up to 13.5 or above.

do this test like first thing in the morning when the car has been sitting all night.

also, when a car comes into my shop and they tell me the car wouldn't start that morning, after i make sure the battery is okay, i check the charging, usually it will be at 14 volts but ill let it run for about 10 minutes with the ac fan on high, radio turned up, high beams on, flashers on. a lot of times the alternator will quit under that much load.