How to size backup power for a CPAP safely
A CPAP is a medical device. That changes how you shop — not because the math is complicated, but because the stakes of getting it wrong are different from a dead phone charger.
This guide does one thing: capacity math for a CPAP during a power outage. It tells you how to calculate what battery size your device needs for a night, and what to verify with your manufacturer before you buy anything.
The safety framing first
Everything in this article is an Estimate with the assumptions shown. No figure here is a guaranteed runtime. Actual runtime varies with your pressure settings, humidifier and heated-tube settings, ambient temperature, the station you buy, and the efficiency of how it’s connected.
Before an outage plan becomes your plan:
- Verify your device’s draw with the manufacturer. Your model’s manual or spec sheet is the authority.
- Talk to your clinician or device manufacturer about device-specific questions.
- Test your setup at home before an outage, on a night when the grid is fine and you can switch back.
- Have a non-powered backup plan — what you would do if the battery plan fails at 3 a.m.
The numbers: what a CPAP actually draws
~60W without the humidifier and heated tube. That’s the figure most capacity planners use for a CPAP running pressure only (Estimate — verify yours).
~90W or more with humidifier and heated tube on. The humidifier setting changes the answer more than which machine you own (Estimate).
The worked example
Assume: 8 hours of sleep, 60W draw, 85% inverter efficiency.
Step 1 — nightly energy the CPAP consumes: 60W × 8h = 480Wh (Estimate)
Step 2 — what the station must hold: 480Wh ÷ 0.85 ≈ 565Wh of station capacity (Estimate)
The practical takeaway: a ~500Wh station is the floor, not the ceiling. A 1,000Wh-class station is the comfortable answer for 8 hours at 60W.
With the humidifier on high (~90W+): 90W × 8h = 720Wh ÷ 0.85 ≈ 847Wh (Estimate).
| CPAP setup | 8h need (Estimate) | Station class |
|---|---|---|
| Pressure only, humidifier off (~60W) | ~565Wh | ~500Wh is the floor; 1,000Wh is comfortable |
| Humidifier + heated tube (~90W+) | ~847Wh+ | 1,000Wh class |
Why humidifier settings matter more than the machine
Turning the humidifier from off to high can add 30–40W to the same machine — a 50%+ increase on one device. A 12V DC adapter (sold by most CPAP manufacturers) wastes less energy than running through the AC inverter.
What this guide does NOT do
- No medical advice. We are not clinicians. Nothing here replaces your doctor, your sleep specialist, or your device manufacturer’s guidance.
- No guaranteed runtimes. Every number on this page is an Estimate.
- No “safe for your condition” claims. That determination belongs to you and your care team.
- No electrical or device-modification advice. Use manufacturer-approved adapters.
A note on battery chemistry for nightly use
If you’ll run a CPAP on battery regularly, chemistry matters. A LiFePO4 battery rated for 3,000+ cycles (the AC180, DELTA 3, and C1000 Gen 2 all use LiFePO4) tolerates years of nightly cycling. An older NMC unit rated for ~500 cycles would reach its rated cycle life in under two years of nightly use.
Your pre-outage checklist
- Confirm your draw with the manufacturer.
- Decide your humidifier setting in advance.
- Test at home before an outage.
- Have a non-powered backup plan.
- Talk to your clinician or manufacturer for anything device-specific.
What size station, concretely
For 8 hours at pressure-only settings (~60W), the math lands at ~565Wh — so look at the 1,000Wh class for real margin:
- BLUETTI AC180 — 1,152Wh, 1,800W continuous. $499.00 (checked 2026-10-15). Check price [Affiliate link — we may earn a commission.]
- EcoFlow DELTA 3 — 1,024Wh, 1,800W continuous, 5-year warranty. $629.00 (checked 2026-10-15). Check price [Affiliate link — we may earn a commission.]
- Anker SOLIX C1000 Gen 2 — 1,024Wh, 2,000W continuous. 24.9 lbs. $549.99 (checked 2026-10-15). Check price [Affiliate link — we may earn a commission.]
These are capacity suggestions only — pick based on your verified draw, your clinician’s input, and a home test, not on this list alone.
Your next step
Run your own numbers through the Outage Brief calculator using the CPAP preset.
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