CPAP Backup Battery Guide: Sizing Power for Outages (2026)

By Nacho Iniguez ✦ Updated June 12, 2026

When the grid goes down, most appliances can wait until morning. A CPAP cannot. If you rely on therapy every night, an outage is not an inconvenience, it is a night without treatment. The good news is that CPAP machines sip very little power compared to a fridge or a space heater, so a modest battery can carry you through. The trick is sizing it honestly, and that starts with knowing how many watt-hours your specific setup actually pulls.

This guide walks through the math, the one spec that matters most for safety, and how to stretch a single charge across multiple nights. One thing up front: this is not medical advice. Confirm your machine’s real power draw and any battery compatibility with the device manufacturer, and if your therapy is medically critical, talk to your clinician about a backup plan before you need one.

How Much Power a CPAP Actually Uses

A bare CPAP, just the blower pushing air at a typical pressure of 7 to 12 cm H2O, draws roughly 30 to 60 watts. That is genuinely small, on par with a couple of light bulbs.

The number jumps the moment you add heat. A heated humidifier adds about 25 to 35 watts, and a heated tube adds more on top. With both running, total draw commonly lands between 90 and 120 watts. The humidifier and heated tube together can account for 60 to 70 percent of your machine’s total power use, which is the single most important fact in this whole guide. Heat is expensive. Air is cheap.

Two caveats. Pressure setting and machine model both move the number, and the figures above are general ranges from manufacturers and market sources, not a measurement of your unit. The label on your power brick, or a cheap inline watt meter, will tell you the truth for your exact setup.

Calculating Watt-Hours Per Night

Watt-hours (Wh) are what you actually shop for, because they describe energy over time, not just instantaneous draw. The formula is simple:

watts x hours = watt-hours per night

Run the two extremes for an 8-hour night:

• Blower only, no heat: 40 W x 8 h = about 320 Wh. Many efficient machines on DC dip closer to 240 Wh.
• Humidifier and heated tube on: 90 to 100 W x 8 h = roughly 720 to 800 Wh.

That spread, 240 Wh at the low end versus 800 Wh at the high end, is enormous. It is the difference between a small power station lasting two nights and barely lasting one. This is why the humidifier decision drives every other choice you make here. If you can sleep comfortably with the heat off during an outage, your battery budget shrinks dramatically.

For a setup tailored to your own pressure, hours, and accessories, run the numbers through our battery sizing calculator rather than guessing from a range.

Why Pure Sine Wave Matters

If you take one safety point from this guide, take this one. CPAP machines have sensitive electronics and motor controllers, and many manufacturers specify a pure sine wave power source. The cheaper “modified sine wave” inverters output a choppy, stepped waveform that can cause some machines to run hot, behave erratically, or refuse to start, and it may void warranty coverage.

Every quality portable power station worth buying for this job outputs pure sine wave AC, and LiFePO4 (lithium iron phosphate) chemistry is the current standard for its long cycle life and stable thermal behavior. When you compare options in our best home backup battery roundup, confirm the spec sheet says pure sine wave before anything else. Do not assume it. Verify it, then verify your machine accepts it with the manufacturer.

DC vs AC: The Free Runtime Upgrade

Here is a quiet efficiency win most people miss. When you plug your CPAP into a power station’s AC outlet, the station converts its stored DC battery power up to 120V AC, and then your CPAP’s power brick converts it right back down to DC. That double conversion throws away roughly 15 to 20 percent of your battery.

Many CPAP machines accept a 12V DC input directly through a manufacturer or third-party DC cord. Feeding the machine DC straight from the power station’s car-style port skips the inverter entirely and recovers most of that lost capacity, often 10 to 20 percent more runtime per charge. On a borderline night, that margin is the difference between waking up on therapy and waking up to a dead machine.

One important pairing: most DC cords for CPAP machines disable the humidifier, because the humidifier’s heater needs the higher-power AC path. That is usually a feature, not a bug, during an outage. You lose heat but gain runtime, which is exactly the trade you want when capacity is scarce.

Sizing for Multiple Nights of Backup

Decide how many nights you need to cover, then multiply. Pick a realistic per-night figure first:

• Heat off, DC direct: about 250 to 320 Wh per night
• Heat on, AC inverter: about 700 to 800 Wh per night

Now map that to real capacity. A 500 Wh power station covers roughly one heated night, or about two nights with heat off on DC. A 1,000 Wh class unit, like a 1,024 to 1,070 Wh station, comfortably covers multiple no-heat nights, or a heated night plus margin for phone charging and a lamp. Always pad your estimate. Cold weather, an aging battery, and higher pressure settings all eat into rated capacity, so do not size to the exact edge.

If you want recharge capability during a long outage, a power station that accepts solar input lets you top up by day and run therapy by night. To see whether that pencils out for your situation, our solar plus battery ROI calculator and time-of-use arbitrage calculator frame the broader cost picture beyond just the CPAP.

Portable Options and What to Check

For pure portability, larger CPAP-specific lithium battery packs exist and are sized in watt-hours just like a power station, so the same math applies. They shine for travel and camping. For home outage resilience, a pure sine wave power station in the 500 to 1,100 Wh range is usually the better value and does double duty for the rest of the house. The Anker SOLIX F3800 review covers the high end if you want whole-night-plus headroom and the ability to run more than just the CPAP.

Whatever you choose, confirm three things before you trust it: that the output is pure sine wave, that your machine’s manufacturer approves the battery or DC cord, and that the real measured draw of your unit, not a generic range, fits inside your capacity with margin to spare. Test the full setup on a calm night, not during your first real outage.

A Quick Word on Doing This Safely

This guide is informational, not medical advice. CPAP needs vary widely, and only your equipment manufacturer can confirm exact power consumption and battery compatibility for your model. If your therapy is medically critical, plan your backup with your clinician and your durable medical equipment provider, and consider whether your situation warrants a more robust solution than a single battery.

When you are ready to put numbers to your own setup, start with the battery sizing calculator, then browse our full guides and reviews to round out your outage plan. A few minutes of honest math tonight beats a sleepless, untreated night later.