I assume my bad alternator, after having it tested, is the source of my draining battery. The battery is new, less than a week old actually. I'll drive around and my aftermarket voltmeter showed my battery slowly draining from about 12.5 volts charged to around 7 volts before the car stalls. I never thought about it, but why won't my battery light come on? It comes on temporarily like all the other lights when I turn the car on.

 

I've had similar problems and can't say what exactly causes this problem, but I know it happens.

It happened to my son due to a worn-out harmonic balancer, crankshaft pulley (rubber bushing slipping between inner and outer parts) that was not driving the alternator belt. It would put out minimal charge at idle, but when you loaded w/ AC, lights, etc the battery would discharge until ignition would quit w/ never a Alt light to warn of discharging.

My warning would be to make sure your alternator is truly defective, and not a worn harmonic balancer/crankshaft pulley.

good luck

 

Okay, what's a harmonic balancer, and how do I test to see if it and the crankshaft pulley are worn? Would they suddenly go out? I mean, I threw the car in reverse, put it back in drive, and now everything's screwed up.

 

The first question first; the way the battery light works is by equalized voltage.

12 volts postive plus 12 volts positive equals zero voltage difference.

So even though the battery was dropping off the power from the alternator lead wire was equal to the battery voltage, so the light didn't come on.
Shorted internal regulator of the alternator.

Second question second; LOL The main crank pulley has a strip of rubber between the 2 parts of the pulley, it is there to absorb 'harmonic' vibrations.
Sometimes the rubber rots out and the big part of the pulley spins on the smaller part of the pulley, the smaller part being actually bolted to the crank shaft.

 

Well I assume I have a bad alternator since Advance Auto Parts tested the alternator (on the car though) and they said it was dying.