Running a CPAP in an RV or van on battery

A CPAP is one of the easier things to run off an RV or van battery, as long as you know how much the humidifier uses and you skip the inverter where you can. This guide uses the RVWatt calculator’s math to show how many nights you get from a battery and how much solar keeps it going. It is planning information about power, not medical advice.

How much power a CPAP uses

The RVWatt library uses a conservative allowance of 40 W for 8 hours, or 320 Wh a night, running on 12 V. Real machines vary a lot: many draw roughly 10–15 W without the humidifier and 40–60 W with a heated humidifier and heated tube. Your machine’s power supply label is a maximum, not the average; the manual or the manufacturer’s battery guide usually gives a better figure, and a plug-in or DC meter over one night gives the best one.

Nights per battery, with and without the inverter

Running a CPAP through an inverter costs more than the CPAP itself: 10% inverter loss plus about 10 W of inverter idle draw for all 8 hours (80 Wh). Many CPAP makers sell a 12 V DC power cord or converter, which avoids both. These figures are for 8 hours a night on a 12 V battery with no charging.

CPAP setup	Wh per night	Nights on 100 Ah LiFePO4 (960 Wh)	LiFePO4 for one night at 12 V
12 W, no humidifier, on 12 V DC	96 Wh	10.0	10 Ah
12 W, no humidifier, through the inverter	187 Wh	5.1	19 Ah
40 W allowance, on 12 V DC (calculator default)	320 Wh	3.0	33 Ah
40 W, through the inverter	436 Wh	2.2	45 Ah
60 W, heated humidifier, on 12 V DC	480 Wh	2.0	50 Ah
60 W, heated humidifier, through the inverter	613 Wh	1.6	64 Ah

The humidifier and heated tube are the big variables, and the inverter can nearly double the energy of a low-power machine. With an AGM battery used to 50%, expect a little under two-thirds of these nights (600 Wh instead of 960 Wh from 100 Ah). Talk to your doctor or equipment supplier before changing humidifier or therapy settings to save power.

Open the CPAP in the calculator, one night Same at 12 W Same at 60 W

Solar for a CPAP, and for the rest of the rig

On its own, the 320 Wh allowance needs about 106 W of solar in Denver from May to October (October is the weakest month at 3.98 sun hours), or about 185 W in Seattle for the same season, so one 200 W panel either way. A CPAP rarely runs alone, though. Added to the weekender van preset (12 V fridge, fan, lights, pump and phones), the day goes from 830 Wh to 1,150 Wh: about 382 W of solar, still two 200 W panels, and about 240 Ah of lithium for two days. With a 60 W heated humidifier it becomes 1,310 Wh, about 435 W of solar (three 200 W panels) and about 273 Ah.

The travel trailer guide has the same comparison for a trailer with a large 12 V fridge; see solar for a travel trailer. For how many nights other loads leave you, see how long a 100 Ah lithium battery lasts.

Weekender van plus a CPAP, Denver, May–October

Plan for a night when the power fails

If you rely on a CPAP, treat battery power like any other piece of travel gear that can fail. Leave margin rather than sizing to the exact number of nights. Know what happens at the battery’s low-voltage cutoff: the CPAP simply stops. Keep a backup you trust, such as a second charged battery or power station, a generator, or a campground with shore power, and follow your doctor’s advice for nights without the machine.

Cold nights add to the load because humidifiers and heated tubes work harder, and most LiFePO4 batteries must not be charged below 0 °C (32 °F); see LiFePO4 vs AGM for cold-weather options. Use the manufacturer’s DC cord or converter for your model rather than an improvised cable, fuse the circuit that feeds it, and have a qualified RV or marine electrician check any new 12 V circuit if you are not confident with the wiring.

Frequently asked questions

How long will a CPAP run on a 100Ah lithium battery?

About three nights at the calculator’s conservative 40 W allowance for 8 hours on 12 V DC, using 960 Wh of a 12 V 100 Ah LiFePO4 battery. A machine using about 12 W without the humidifier can get about ten nights, and a 60 W heated humidifier setup about two. Through an inverter, expect fewer nights.

Should I run my CPAP through an inverter or on 12 V?

On 12 V DC if your manufacturer offers a DC cord or converter for your model. An inverter loses about 10% and draws about 10 W just by being on, which is 80 Wh over an 8-hour night. For a 12 W machine that nearly doubles the energy, from 96 Wh to about 187 Wh a night.

How much solar do I need to run a CPAP in a van?

For the CPAP alone at 320 Wh a night, about 106 W of panels in Denver from May to October, or about 185 W in Seattle for the same months, so one 200 W panel. Added to a weekend van’s fridge, fan, lights, pump and phones, the day is about 1,150 Wh and needs about 382 W of solar in Denver, so two 200 W panels.

Related guides

Safety: high-current DC is dangerous. A 12 V battery bank can deliver thousands of amps into a short circuit, enough to melt tools, weld rings and watches to terminals, ignite insulation and start a vehicle fire in seconds. Lithium and lead-acid batteries can also vent, burn or explode if overcharged, damaged or charged outside their temperature limits. Remove jewelry, use insulated tools, disconnect the battery before working, fuse every positive conductor as close to the battery as practical with a fuse rated for the battery's short-circuit current (often a Class T for lithium banks), use properly crimped lugs and pure copper cable, and secure batteries against movement. If you are not confident, hire a qualified RV or marine electrician. RVWatt provides estimates only; see our Terms of Use.

These figures are planning estimates from typical appliance ratings and NASA monthly sun averages for a flat, horizontal panel. Your real use will differ with heat, shade, dirty panels and how you actually live in the rig. Follow your equipment manuals and have a qualified installer check high-current wiring.