The short detector on the slide out controller should be post-controller (motor side).
Sounds more like a very bad connection or batteries past end of life.. IE.. When my Original hit 9 years old they had relatively little capacity (30%) of what they had when new.
Batteries have several failure modes. One is HIGH RESISTANCE this can be Mimiced by a dirty connection (high resistance connection) and on my chassis battery that happened 3 times... That sounds like what you got.
Loss of capacity.. that is also a failure mode. a 200 amp hour battery is down to 50 or less
And shorted cell.that is the bad one because with shorted cell it never comes UP and the non-shorted can boil dry.
OH speaking of boil dry.. Check the fluid level (IT's not water) and if needed add DISTILLED WATER to the mix.
