 Battery charging without ALT light, What’s going on? |
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| VaccaRabite |
 Sep 30 2026, 02:06 PM
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En Garde!  Group: Admin Posts: 13,921 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region 
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A friend of mine had his battery pop in his 914. Battery acid everywhere. We got it running last weekend after a year of sitting.
Of note, the alternator light never turns on. BUT, the car is charging the battery at 13.9 volts. How is this possible? My guess is that he has a damaged or failing diode in the alternator, but I thought the battery COULD not charge without the alternator light turning on. So I’m confused. Thanks Zach |
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| VaccaRabite |
Sep 30 2026, 05:02 PM
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#2
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En Garde! Group: Admin Posts: 13,921 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region
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Not my car and I’m currently 100ish miles from it.
I’m not clear on why the battery popped, but I suspect overcharging. On key in, the alternator light does NOT turn on. It stays off throughout startup and driving. By everything I know this means the car should not be able to charge, but measuring across the terminals at idle he’s making 13.9 volts. When the car is off it settles at 12.6 volts. Zach |
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