2000 Pontiac grand am 2.4 automaticbattery light came on while driving. took battery and alt to Autozone. alt tested good. battery tester not working. warrantied battery anyway. so, good alt and new battery. checked for loose/bad connection. all seem fine.when I start car in the morning I can drive 10 min the the battery light comes on. I can accelerate 1500+ rpms and light goes off but back yo idle the battery light comes back on.too car to orilleys auto and had them test on car. battery good. alt diodes good. receiving low voltage at 11.78. was told alt bad???? was it a bad bench test or is could there be something else???
Is the belt tight enough ? After 12 years the belt may be due for replacement.
Sounds like the alternator is charging but not enough, you need 13.5 to 15 volts at the battery when the engine is running to keep everything going. Change the alternator and you should have solved the problem.
