What it does
The battery disconnect switch separates the house batteries from most of the RV's 12-volt system. Turn it off and the small loads that drain batteries in storage are cut off.
Where to find it
Often near the entry door (sometimes labeled "battery disconnect" or "battery"), or in the battery compartment as a rotary switch. Motorhomes may have separate switches for chassis and house batteries.
Common confusion
"Off" may not mean everything off. On some RVs, a few loads are wired ahead of the switch, or the solar controller connects directly to the batteries. If the battery still drains with the switch off, something is wired around it.
Plugged in with the switch off. On some RVs, turning off the disconnect also stops the converter from charging the batteries. On others, charging continues. Check your manual.
Bumped switches. A disconnect switch left off is one of the most common "dead battery" calls we get.
Using it in storage
Charge the batteries, turn off the disconnect, and check voltage over a few days to confirm nothing is still draining. See storage in Florida summer.