Got the battery idiot light yesterday, but it turned off. This morning it was back on at startup.

Voltage across battery when engine off is 12.82 Vdc, and when running at idle (~ 600 rpm) it drops to 12.32 Vdc....Alternator bad ?

UPDATE: AutoZone parking-lot check indicates battery has one dead cell AND alternator is also bad.

Question: Can the bad battery CAUSE the alternator to charge low....to simulate a bad alternator (wishful thinking, I admit).
I hate to pull that alternator and find it's OK under a good load.

 

had something like that happen on my caddy. brand new battery only two months old. stored it over the winter. then it wouldnt keep a charge, was thinking it was possibly the alt too. everything was fine with a new battery. theyre easy to replace too. the alternators are a pita, and expensive.

 

I replaced the alternator and all is well, apparently. I want to have the battery and charging system re-checked again soon, just to be sure.

The alternator is a PITA to change, like you said, but the new one was FREE ...the bad one was under lifetime warranty. I bought it in Nov 2011 and still had the purchase info. ALWAYS save your receipts on purchases like this...you never know, and certainly I expected more than 22 months out of a part like this.