Alternator or Battery problem?
 

The past 3 years I have had an undersized battery for the Bonny. Never had any issues with it. Recently I have noticed that if all accessories( Lights, fans, defogger, wipers etc.) are one while in drive at itle the volts drop to the line before the red. Sometimes it will drop below that but never in the red. Once I start driving volts move up to normal. I have even checked with volt meter and scanner and numbers check out good. Once warmed up volts are 13.8 and at idle with everything on in park volts drop to 11.8-12.2. I just swapped out alt with a known good one and it appears to be about the same. Would an undersized battery not be able to keep up with the power drain or is it time for a new battery and/or alt? I know I could just take it to Autozone to test but I don't trust them 100%.

I suggest the correct sized battery. It's normal to see a voltage drop at idle. A larger battery will help when at idle.

That's what I thought. Not enough reserve to power all the accessories. Time for new battery! Thanks!!

If it helps any.. I see the same on a new alternator etc. At idle if you are running enough accessories the draw is more than the alternator can power. This is because the alternator is spinning slowly and can only generate X amount of power.