Lately I've been experiencing an issue regarding my charging system. When I measure voltage at the battery terminals while engine is idling, it's a pretty low 12.5v~ or so, when cooling/HVAC fans come on it can go below 12V completely. Revving the engine can top me out at 13V.
I wanted to check my alternator's output directly, so I found the positive cable, uncovered the rubber housing, and put my multimeter lead on the nut, then I grounded it on part of the alternator housing (and again on the engine block) -- the alternator read an output of 14+ volts.
Does this mean the alternator is good but the battery is just not getting enough power? Because as I said the alternator DOES charge the battery slightly, but all of the power doesn't seem to be getting to the battery.
One thing I did notice was the ground wire from the negative battery terminal is exposed, and oxidized (it's green), I have been suspicious of that ground but before I replace it I want to know if that could possibly cause low voltage, or if the solution might be in another area.
So to summarize:
1) Is my method of testing alternator output correct? And does that mean my alternator is outputting good power?
2) Could a bad ground cable be responsible for the described issue?
Vehicle is a 2000 Acura TL.
EDIT: Problem was fixed, it was the ground cable. The connection was corroded very badly -- keep your grounds CLEAN. This improved my car 100%, everything in the car is controlled by electronics, now that it has proper supply its great.