Camping with CPAP: sizing a battery for three nights

Three nights off the grid sounds daunting until you do the sums. CPAP power use is modest, and the biggest lever is one setting you control: whether the heated humidifier is on.

The maths

These are typical figures; your machine, pressure and room temperature change them, and other models differ. Look for the rated wattage in your user guide, or measure with a plug-in power meter for a night at home before you go.

Ways to cut the number

Skip the heated humidifier in warm, humid weather, or use it on a low setting. It is the single biggest saving. Use the DC cable your machine supports rather than an inverter, which wastes energy converting twice. Keep the machine in a warm place (not frozen) and the battery out of direct sun. A lower-power machine or a travel model also helps, though that is a purchase decision.

Choosing and carrying a battery

Capacity is quoted in watt-hours, usually at nominal voltage. A larger pack gives more nights but weighs more. If you will fly with it, airlines follow FAA-style limits on lithium spares: up to 100 Wh is generally allowed in carry-on, 101 to 160 Wh needs airline approval (two spares at most), and over 160 Wh is not allowed. Always check your airline, because rules differ by carrier and country. The free battery calculator does the sum for you.

Logging a trip

Use Notes on the nights you are camping, so changes in altitude, sleep position or humidifier use are on the chart next to AHI and leak. A few nights away often look different from home, and the context helps you read them fairly. See travelling with CPAP for more planning tips.