I've done this for years. My CPAP runs on 12VDC so it works directly from 12v in my RV (recharged by solar panels) or from a portable 12v Lithium battery pack t

I've done this for years. My CPAP runs on 12VDC so it works directly from 12v in my RV (recharged by solar panels) or from a portable 12v Lithium battery pack that gets me through about two nights without recharging. No inverter needed, and I don't use the humidifier on battery power. Unfortunately I just got a new CPAP that uses 25 VDC, so I'll have to build or buy a DC-DC boost converter for it. Slightly annoying, but not a big problem.