Dead chassis batteries are common in many RV's - that's because some mfg attach alarms, electronics to the chassis batteries and because newer cars have more electronics which consume power even when the rigs not operating. Many get around that problem buy purchasing an inexpensive device called Trik L Charge which allows the chassis battery to charge while your rigs plugged into shore power.
Performing a normal battery charge should not require you to disconnect anything on any rig. I disconnect my rig from shore power anytime I am working on batteries.
