Batteries Overcharging Badly

[pgchin]

Two votes for the new regulator not being rewired properly to retrofit the bird's electrical system, I believe David may have nailed your initial issue. This has been seen before. Also, if you and he (your mechanic) have time I'd disconnect each battery both the chassis(group 31"s) and the house (4D's) and load test each one as well as meter each one for voltage. Each cell of a battery you loose will drop you 2 volts per cell/batt......... overcharging batteries, even new, will cause them to prematurely fail and short inducing new issues you did not have before and cause both you and he to "chase your tail", install more parts, etc......................good luck and sorry you missed you special trip.......it is a bummer!
FWIW, just one shorted cell in just one battery of the entire string will cause both the 50DN or the inverters to try and satisfy the load, keep charging all batteries and they will ALL overcharge, get hot, start warping plates, etc.
My apologies for the late response, I've been traveling for 5 days and was not on the internet.............