I have camped with one since 1994. I use a CPap. At first, I bought some extension or lamp wire from a roll at the hardware store, clamped some flat brass/copper adapters, that fit over the battery posts in the battery compartment, onto the wire ends. I drilled a few small holes through wall and floor in bedroom, ran the wire then attached to cig lighiter. I then hooked up the Cpap w/adapters.
I changed that sevearl years ago when I went to two 6 volt batteries for the 5ver. Since I still had a couple of 12v batteries, I just put one in the bedroom , hook an adapter w/clamps to the battery w/the female cig lighter on other end (bought at walmart for less than $10) then plug a cheap 175 watt inverter (about $30) into that. Then I just plug my regular CPap power cord into the inverter. It will ususally last 3 days or more per/battery.