Noticed this when I pulled my high output alternator out to have it repaired. Put my stock alt in, had a wet cell under hood and agm in the trunk. I did have two amps hooked up while the stock alt was in but drop didn't seem to be from the amp pulling. I disconnected both amps and ran it for two weeks and problem persisted. It'll go from 14.4 to 12.7/8 to 13 then back randomly. I reinstalled my ho alt about a week ago and the problem is still there. Doesn't appear to be any loose connections, but I've noticed a lot of corrosion on both terminals for the wet cell since putting the regular alternator in and I've had that battery for over a year prior with no corrosion? Any suggestions?