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Battery discharge when driving

Day one: check gauge light comes on, 20 miles later, radio dies, air bag lights come on, battery gauge plumets, car dies, I get a tow.
Day two: husband puts in a new battery
Day three: drive 25 miles to work, battery gauge light comes on, plumets down, get a tow, start the car and battery gauge is back up but I don’t want to drive the darn thing.
Day four: any ideas?

Sounds like a bad alternator first guess. A reliable analysis for a reliable repair.


Okay thanks will get it checked!

Yup, I agree emphatically.
Have the alternator load tested. Post back with the results.


Not the alternator…Ground wire?

Could be any of the heavy cables that attach to the battery, corroded.

Or you could have a partial short somewhere in the electrical system, draining more current than the alternator can supply. But this seems unlikely, as that is a huge amount of power and heat.

Or whoever tested the alternator did it incorrectly.

Edit: get a $10 voltmeter that plugs into the cig. socket. Use that to monitor the battery voltage under various conditions. Eg, car on but not started (should be about 12.6 volts) attempting to start (10.5 volts or higher) or with engine running (12-15 volts0.

I don’t believe the charging system will test good if a ground wire is missing.

If the low voltage warning light is on and the battery discharges as you drive you have a charging system problem. The charging system should be inspected and tested.

I had this same problem on my Corolla, alternator tests ok, but not charging battery. Turned out the wire between the alternator and the battery got buggered up with battery acid from a leaking battery. Soldering that back together solved the problem.

Ask your shop to measure the main alternator voltage output with the engine running. It should match closely to the voltage at the battery posts. Usually in the 13.5 - 16.0 volt range. If there’s a difference of more than 0.5 volt between what you measure at the alternator vs the battery, you likely have a problem in that connection. I think there may be a fuse in that path also on some vehicles. So that’s another possibility, a blown fuse. It’s often called a “fusible link” rather than just a “fuse” b/c of the large currents involved.