Would like to boondock in our RV but need to power a CPAP for the wife. Looked at the label and her CPAP draws 6.67 amps. How large of a portable power station would we need? We can recharge it during the day with a generator.

2 group 31 batteries wired as 24 volts should do it, you'll need 313 amps (total) to run it for 9 hours at 24V DC. Plus you'll need the inverter to convert it to 125 volts AC.

That's 313 amp-hours, not amps. If it draws 6-2/3 amps @ 125VAC, then you'd draw 34.7 amps from the batteries @ 24VDC. Be sure to check the efficiency of the inverter since if it's not 100% (and none of them are), you'll be wasting some power as heat during that 24VDC-to-125VAC conversion process.

If there is not a big price difference you could consider deep cycle batteries, group 27 instead of group 31.

Label is likely going to show max current draw on start up and with humidifier on highest setting. Not really an accurate number to use to determine how much battery capacity you need. More telling is the wattage.

CPAPS generally don't use much power at all. It is just a fan and some electronic circuits. What uses most power is the heated humidifier. My experience has been that unless I am in a VERY low humidity area (like less than 25%) I can get by with just "passover" humidification- water in the tank but heater turned off.

What CPAP does your wife use? Most of the major brands already have 12v power cords/converters available so if your RV already has a battery bank you may not need anything other than their adapter (usually in the $85-$125 ballpark)



If you really want a standalone battery option, I have a ResMed AirSense 10 and use this for power outages:

https://www.amazon.com/gp/prod..._title?ie=UTF8&psc=1



It is good for 2-3 nights when fully charged and is not "dedicated" to the CPAP so can be used for other things as well. Also no where near the weight and complexity of deep cycle batteries, charger (need ventilation), converter, etc.