Charged battery quickly drains while driving, but battery and alternator ok at idle
I don't know what to check next. I charge the battery with an a.c. charger. I
can start the car and drive off to work. But along the way, the battery drains
to the point where the car will not run.
First the battery light comes on, and I start getting nervous. A while later the
the ABS light comes on, and my stress increases. Then the "brake" light
comes on, and panic ensues. Finally, the speedo and gauges drop to zero,
and I know the gig is up. When I am lucky I have just pulled into the parking
lot before the engine stops. The battery has about 9 volts after these 15
minutes of driving. I charge the battery during work, and repeat the process
to get home.
Here is what I have learned.
The battery is ok. It will charge with an a.c. charger and the parts store
checked it with a load tester.
The alternator produces about 13.5 volts at the alternator output terminal at
engine idle. (This is actually a "new" used alternator I replaced. I now
suspect the original alternator is ok as well)
There is acceptable voltage drop across the positive and negative sides of
the wires to the alternator. Thanks Youtubers.
It seems that something in the alternator controls (from the four-connector
plug) stop it from charging the battery while I am driving.
What should I check next ? How can I verify that it is something from the
alternator controls, and if it is, how to fix it ?
Thanks
