My 95 CTD is charging both batteries between 17-18 volts. I am verifying this with a meter at the batteries. The truck gauge is showing just over 15, I am not getting any warning lights and the truck seems fine other than this. Where should I start to diagnose this problem?

 

Hmm, I may have the same problem- I will check mine as I put in 2 new optima's and the vent cap is seeping acid- something agm batteries never do

 

overcharging on my 12v turned out to be a bad pcm..

you could try and external regulator, but it didn't work out well for me..., yet my truck also showed the gen light on when it went..

basics also tell me, load test both batteries separately.. one might be bad, causing the pcm to send an over charge to compensate for the bad battery...