CPAP backup power: watts, battery size and runtime

Updated 2026-10-31 · Sources linked inline

Read this first. This page is general planning information for a CPAP, APAP or similar sleep-apnea machine. Check your own device's rating, and ask your provider or equipment supplier what backup power they recommend for your machine and prescription. This page is not for life-support planning. If you depend on a ventilator, oxygen concentrator or any other equipment where an interruption could be dangerous, talk to your provider and your utility about a plan before an outage, not after.

A CPAP machine uses roughly 10 to 75 watts, depending on the model, your pressure and whether the heated humidifier and heated hose are on. For eight hours that is about 90 to 600 watt-hours (Wh) at the machine, and about 100 to 700 Wh of battery once you allow for losses. The heated humidifier and heated tube are the big variable. Everything below shows where those numbers come from and how to find yours.

How this guide was made: this is a research guide built on manufacturer specifications and federal guidance, with sources linked throughout. We haven't bench-tested any of the equipment mentioned, and we don't claim to. We are not medical professionals.

The published numbers

Start with what the manufacturers publish for current machines:

Notes on reading these:

• ResMed's "typical" and "peak" figures cover the device with its humidifier and heated tubing. Your draw can be far lower with those off.
• The VA figures are higher than the watt figures because the AC power supply has a power factor below 1. If you use an inverter or UPS, check that its rating covers the VA, not just the watts. It rarely limits you, but check.
• Champion's 120 W is a generic ceiling. ResMed's own peak for the AirSense 11 is lower, at 73.2 W. Using the generic range oversizes, which is the safe direction.

The Champion rows are also in our appliance wattage chart.

What the heated humidifier costs you

ResMed's battery guide for the older AirSense 10 lists measured current draw at 12 V DC through its DC-to-DC converter, at a pressure of 10 cm H2O (ResMed battery guide). We converted those amps to watts (watts = amps × 12 V) to show the pattern. This is the AirSense 10, not the 11, so treat it as an illustration of the pattern, not as your machine's number:

The pattern holds for most machines: at high settings, the humidifier and heated hose can multiply nightly energy roughly four to five times (11 W dry versus 44 to 59 W in the table above). Running without them is a comfort and clinical question, so ask your provider first.

Philips doesn't publish a typical-watts figure for the DreamStation 2 in its instructions, so for that machine use the generic Champion range above and your own provider's guidance.

Measure your own machine

The most reliable number is your own, taken the way you use it. We haven't measured any CPAP machine ourselves; these are the steps the manufacturers and meter makers describe:

1. Read the label and manual. The power supply label shows a maximum, not typical use.
2. Use a plug-in meter. Put a watt meter (Kill A Watt style) between the wall and the power supply for a full night at your normal settings. Multiply the morning kWh reading by 1,000 for Wh.
3. Repeat with the humidifier settings you would use in an outage.

The math: how many watt-hours for 8 hours?

Wh needed = watts × hours ÷ efficiency. Our power station runtime calculator assumes 85% efficiency, a planning figure that covers inverter and battery losses. It is an assumption, not a measurement. Examples for 8 hours:

Plan on roughly 565 Wh for a humidified night using the generic 60 W figure, or about 530 Wh from ResMed's typical for the AirSense 11. A dry night can be a few hundred watt-hours less. Round up, and multiply for several nights.

Your options

This page doesn't recommend a brand. "Pure sine wave" AC output is a spec to look for: ResMed's battery guide recommends a pure sine wave inverter rated 300 W continuous and 500 W surge for the older machines it covers, and says certain older heated humidifiers must not be used with inverters at all. Your machine's manual is the authority.

Example: one power station, several nights

EcoFlow lists the DELTA 2 at 1,024 Wh (EcoFlow). At 85%, about 870 Wh is usable. For a CPAP alone, that is:

That is the CPAP alone. Anything else on the same battery shortens it; the power station sizing worksheet covers the full load.

Cut the draw without guessing

• Turn off the heated tube first. In the AirSense 10 numbers, going from the heated ClimateLine Air tube at 30 °C to unheated SlimLine tubing at the same humidifier setting saves about 15 W (59 W to 44 W). Ask your provider whether that is appropriate for you.
• Humidifier setting. Settings 4 versus 8 differ by roughly 16 W in ResMed's table.
• Charge before you need it. Batteries self-discharge, so top up before storm season.
• Plan the recharge. A longer outage needs a bigger battery or a second source, such as solar or a car trip to charge.

Water for the humidifier

If you use the humidifier, you need water. ResMed's guide specifies distilled water for the standard AirSense 11 tub, and Philips says to use room-temperature distilled water in its humidifier tank. Keep a gallon of distilled water in your outage kit.

Battery safety

A power station stores a lot of energy. The U.S. Fire Administration says to store lithium-ion batteries at room temperature when possible, not to charge them below 32 °F or above 105 °F, and to stop using any that smell, change shape, leak or get hot (USFA). Practical steps:

• Use a hard, non-flammable surface away from bedding and curtains.
• Use only the charger the maker supplies.
• Don't use a damaged or swollen battery.
• If a battery smokes or ignites, leave and call 911.

Keep any generator outdoors, more than 20 feet from openings. For the rest of the plan, see the Alabama outage checklist and the winter storm checklist.

Questions to ask your provider

1. What is my machine's actual power draw at my settings?
2. Do you have a DC cord, converter or approved battery for my model? Is there a battery you recommend for it?
3. Is it safe to use the humidifier or heated tube on battery power?
4. If I can't use therapy for a night or more, what should I do?
5. Does my utility offer a list for customers with medical equipment? (Programs vary; ask, and don't assume priority restoration.)

Summary

Run your numbers in the power station runtime calculator and ask your provider before the storm.