Hi!
Few weeks ago I noticed that at idle my battery voltage is jumping. It falls to 12V range or even to 11.5V. When I drive, everything is OK. I know that clutch in my AC compressor is slowly dying, but it should not cause it (i guess). I is happening mostly on high loads (combination of any two or more: low beams, high beams, defogger and AC). When I add wipers then it just stays at 12V range (no jumping). But it also happens with normal power load. I replaced the alternator, swapped the battery for few minutes and the problem did not disappear. I have 2005 EVO with stock audio (no music system).

 

bump

 

You might want to get some documentation on what the voltage is supposed to be during different events. I went thru this on a pontiac torrent and found it was perfectly normal. The battery will hold a different charge when ur lights are on, right at start up, and at a few other times. Usually when lights are on it's higher? BUT, that being said I don't think it should ever be below 12? If it is then you have something draining ur car most likely if youve already replaced the alternator and it's still low.

 

sorry, didn't notice that you replaced the alternator. still something is wrong with wiring (short circuit?) maybe the battery is bad? are you sure the other alternator is good?

 

You swapped the alternator with a new or a used one? Could also be a grounding issue or still a alternator that is on it's way out again.

 

alternator was used, but i just installed third (used) one with the same result