CPAP battery sizing is the process of matching your machine's watt-hour demand to a battery's usable capacity so it runs a full night without cutting out. In short: multiply your CPAP's wattage by your sleep hours, then add a 10–20% buffer for conversion losses. New to portable CPAP power? Start with our what is a CPAP battery explainer to understand watt-hours, voltage, and battery chemistry before diving into the math below.
Why CPAP battery sizing matters
Buying a CPAP battery without knowing your power draw is like buying a gas can without knowing your tank size. Too small and you wake up at 3 AM with no therapy. Too big and you overpay for capacity you'll never use — or haul extra weight on a trip.
This 2026 guide walks you through the exact math, gives you a model-by-model runtime table, and shows which LiFePO4 batteries match each tier — so you buy the right battery the first time.
Step 1: Find your CPAP's power draw
Check three places for your machine's wattage:
- The power supply label — flip over your AC adapter and look for "Output" in watts
- The machine's clinical menu — some machines (like ResMed AirSense 11) show real-time power draw
- The manufacturer spec sheet — search your model + "specifications"
Typical power draws by configuration
| Setup | Power draw | Notes |
|---|---|---|
| CPAP only | 15–30 W | Pressure-dependent |
| CPAP + humidifier (low) | 30–45 W | Humidity level 1–3 |
| CPAP + humidifier (high) | 45–65 W | Humidity level 4–6 |
| CPAP + humidifier + heated tube | 50–70 W | Maximum comfort |
| BiPAP | 25–50 W | Higher pressures = more draw |
| BiPAP + humidifier | 50–90 W | Varies widely by model |
Power draw by popular CPAP model
| Machine | Without humidifier | With humidifier + tube | Adapter wattage |
|---|---|---|---|
| ResMed AirSense 11 | ~18 W (planning figure) | 28–48 W, plus 5–15 W for the tube | 65 W |
| ResMed AirSense 10 | ~15–22 W | 50–80 W | 90 W |
| ResMed AirMini | ~6–7 W typical | N/A (waterless HME) | 27 W peak |
| DreamStation 2 | ~10–20 W | 40–70 W | 65 W |
The AirSense 11 ships with a smaller 65 W adapter than the AirSense 10's 90 W unit. The AirMini is the most battery-friendly option at just 6–7 W typical draw. If the AirSense 11 is your machine, our guide to the best AirSense 11 battery matches specific packs and DC cables to that 65 W adapter. For detailed wattage breakdowns, see our CPAP power consumption guide.
Runtime by battery size and CPAP model (at 10 cmH2O)
This table shows estimated usable runtime hours with one consistent rule: DC-direct batteries deliver about 87.5% of rated capacity (the midpoint of 85–90%), and power stations running the CPAP from their AC outlet deliver about 75% (the midpoint of 70–80%). Runtime = rated Wh × efficiency ÷ watts. The AirSense 11 figures are our site baseline of 18 W dry and 48 W with the humidifier on high. Values under 20 hours are rounded to the nearest half hour; longer values to the nearest hour.
| Battery (Wh) | Path | AirMini (7 W) | AirSense 11 dry (18 W) | AirSense 11 + hum. high (48 W) | AirSense 10 + hum. (55 W) | BiPAP + hum. (70 W) |
|---|---|---|---|---|---|---|
| 99.9 Wh (EASYLONGER ES270) | DC | 12.5 hrs | 5 hrs | 2 hrs | 1.5 hrs | 1 hr |
| 150 Wh (NiteOwl) | DC | 19 hrs | 7.5 hrs | 2.5 hrs | 2.5 hrs | 2 hrs |
| 266 Wh (Renogy power bank) | DC | 33 hrs | 13 hrs | 5 hrs | 4 hrs | 3.5 hrs |
| 297 Wh (Bluetti X30 / Yeti 300) | DC | 37 hrs | 14.5 hrs | 5.5 hrs | 4.5 hrs | 3.5 hrs |
| 288 Wh (Anker SOLIX C300) | AC | 31 hrs | 12 hrs | 4.5 hrs | 4 hrs | 3 hrs |
| 384 Wh (SUPA LiFePO4) | AC | 41 hrs | 16 hrs | 6 hrs | 5 hrs | 4 hrs |
| 512 Wh (Jackery Explorer 500 v2) | AC | 55 hrs | 21 hrs | 8 hrs | 7 hrs | 5.5 hrs |
| 614 Wh (Bluetti X60) | AC | 66 hrs | 26 hrs | 9.5 hrs | 8.5 hrs | 6.5 hrs |
| 1024 Wh (EcoFlow DELTA 3 / Bluetti Elite 100 V2) | AC | 110 hrs | 43 hrs | 16 hrs | 14 hrs | 11 hrs |
| 2048 Wh (EcoFlow DELTA 3 Max) | AC | 219 hrs | 85 hrs | 32 hrs | 28 hrs | 22 hrs |
The bottom line: If you run the humidifier on high through an AC outlet, you need roughly 500 Wh for a full 8-hour night. Dry, a 150–300 Wh pack covers one night for most ResMed and Philips machines. If you are sizing for several nights in a row, the 2 kWh tier is where multi-day outage stations start; our best solar generator for CPAP guide compares those 2–4 kWh stations and solar bundles. For an interactive version, use our CPAP battery runtime calculator, or see how long a CPAP battery lasts in a power outage for real-world scenarios.
Step 2: Calculate watt-hours needed
The CPAP battery sizing formula is straightforward:
Wh needed = Power draw (W) × Hours of sleep
Examples for an 8-hour night:
- 20 W × 8 hrs = 160 Wh (AirSense 10 no humidifier)
- 28 W × 8 hrs = 224 Wh (AirSense 11, humidifier low)
- 48 W × 8 hrs = 384 Wh (AirSense 11, humidifier high)
- 55 W × 8 hrs = 440 Wh (AirSense 10 with full humidifier)
- 75 W × 8 hrs = 600 Wh (BiPAP with humidifier + heated tube)
Worked walkthrough: ResMed AirSense 11 with humidifier
Let's size a real setup step by step using 2026 numbers.
- Draw: 48 W (AirSense 11 with the humidifier on high, our baseline figure; measure your own with a plug-in watt meter)
- Target runtime: 8 hours
- Raw Wh: 48 × 8 = 384 Wh
- Inverter buffer (AC power station, ~75% usable): 384 × 1.33 = 512 Wh minimum
- Cold-weather buffer (camping at 40°F): 512 × 1.15 = 589 Wh
- Match to catalog: The Jackery Explorer 500 v2 (512 Wh) covers the night only at room temperature with no margin; a 614 Wh Bluetti X60 or 1024 Wh Bluetti Elite 100 V2 gives comfortable margin.
If you drop the humidifier and use DC-direct instead, the same machine needs about 18 W × 8 hrs × 1.15 = 166 Wh, less than a third as much. See our humidifier battery drain analysis for the full breakdown.
Step 3: Add your buffer
Real-world batteries don't deliver 100% of their rated capacity. Depending on delivery path and chemistry, plan on losing 10–25%:
| Scenario | Buffer to add | Why |
|---|---|---|
| DC-direct (12V/24V cable) | +15% | About 85–90% of rated capacity is usable; some cable and converter loss |
| AC power station (pure sine inverter) | +33% | About 70–80% usable (75% midpoint) after inverter idle draw and AC/DC conversion |
| Modified sine wave inverter | +25–30% | CPAP motors run hot on modified sine — avoid if possible |
| Cold weather (below 50°F / 10°C) | +15–25% | Li-ion cells lose usable capacity; LiFePO4 loses less |
| Battery aged 2+ years | +10–15% | Calendar aging reduces usable Wh |
LiFePO4 packs (Goal Zero Yeti 300, Anker SOLIX C300 288Wh, SUPA 384Wh, Bluetti Elite 100 V2 1024Wh, Bluetti Elite 200 V2 2073.6Wh) hold capacity better in cold and last 3,000–4,000+ cycles — roughly 4–5x the cycle life of standard Li-ion. For the full chemistry comparison, read LiFePO4 vs Li-Ion for CPAP.
Adjusted formula: Wh needed × buffer multiplier = Battery size to buy
Example: 224 Wh × 1.33 = 298 Wh minimum (for AC power station use at room temperature)
Step 4: Match to available batteries
| Your calculated Wh | Recommended battery tier |
|---|---|
| Under 100 Wh | Purpose-built CPAP battery (Pilot-24 Lite View on Amazon, EASYLONGER ES270 View on Amazon, Zopec Explore Mini View on Amazon) |
| 100–250 Wh | Small power station or dedicated CPAP battery (Bluetti X30 View on Amazon, Anker SOLIX C300 View on Amazon, NiteOwl CPAP Battery View on Amazon) |
| 250–500 Wh | Mid-range power station (EcoFlow RIVER 2 View on Amazon, Jackery 500 View on Amazon) — see our best power stations under $200 roundup |
| 500+ Wh | Large power station (EcoFlow DELTA 3 View on Amazon) or multi-battery setup |
See our best CPAP backup batteries guide for detailed reviews, or read the Zopec battery review for a deep dive on the most popular purpose-built option.
NiteOwl CPAP Battery Backup (2nd Gen, 150Wh Swappable)
$287.01
Check price on Amazon
Anker SOLIX C300 Portable Power Station (288Wh LiFePO4, 300W AC)
$329.99
Check price on Amazon
BLUETTI Elite 100 V2 Portable Power Station (1024Wh LiFePO4, 1800W)
$499 – $899
Check price on Amazon
Pro tips to reduce power draw
If you want to stretch your battery further, these changes make the biggest difference:
- Turn off the heated humidifier — saves 10–30 W; use an HME filter instead
- Turn off the heated tube — saves roughly 5–15 W; use a fleece hose cover for warmth
- Lower your humidity setting — each step down saves 3–8 W
- Use EPR on ResMed machines — the "off" setting draws slightly less power than EPR level 3
- Use DC-direct power — skip the AC inverter and save 10–15% of battery capacity. Our DC power adapter guide explains the cables you need, and the compatibility guide covers which machines support DC input.
For a deeper look at how the humidifier affects runtime, see our humidifier battery drain analysis.
Real-world example
Setup: ResMed AirSense 10 AutoSet, pressure 12 cmH2O, humidifier off, DC power cable
- Power draw: ~22 W
- Sleep time: 8 hours
- Wh needed: 22 × 8 = 176 Wh
- Buffer (15% for DC): 176 × 1.15 = 202 Wh
- Recommendation: Anker SOLIX C300 DC (288 Wh), running the DC cable from its 12V socket — one full night with room to spare
With humidifier on high:
- Power draw: ~48 W
- Wh needed: 48 × 8 = 384 Wh
- Buffer (33% for AC): 384 × 1.33 = 512 Wh
- Recommendation: Jackery Explorer 500 v2 (512 Wh) is the bare minimum for one humidified night; the 1,024 Wh EcoFlow DELTA 3 leaves real margin
What about multi-night trips?
Multiply your single-night Wh by the number of nights. For a 3-night camping trip at 202 Wh/night (DC-direct, no humidifier), you need about 606 Wh.
Options:
- One large battery: EcoFlow DELTA 3 (1,024 Wh) handles about 4–5 nights at 22 W
- Battery + solar panel: A 100 W panel recharges ~300 Wh during a sunny day
- Two smaller batteries: Bring two Anker SOLIX C300 units (288 Wh each) and alternate nights
Planning a camping trip? Check out our CPAP camping setup guide for the full off-grid gear list, or our CPAP backpacking guide if you need to keep total pack weight to a minimum.
What to do next
- Measure your actual power draw — use a watt meter or check your machine's clinical menu to get your real wattage instead of guessing
- Run the numbers with our CPAP battery runtime calculator — plug in your wattage, battery size, and sleep hours to get an instant estimate
- Pick a battery from our best CPAP backup batteries guide based on your calculated Wh
- Test for one full night before relying on it — real-world runtime often differs from calculations by 10–15%
If your battery is not lasting as long as expected, check our CPAP battery not lasting fixes for troubleshooting tips.
Related reading
- Best CPAP Backup Batteries — side-by-side battery comparisons and reviews
- CPAP Battery Compatibility Guide — match your CPAP to the right battery
- CPAP Power Consumption Guide — detailed wattage data by machine and setting
- CPAP Battery Runtime Calculator — interactive calculator tool
- Best Power Stations Under $200 for CPAP — budget-friendly options ranked
- Goal Zero for CPAP — sizing Goal Zero power stations for CPAP use
- LiFePO4 vs Li-Ion for CPAP Battery — chemistry comparison and cycle life
- UPS vs CPAP Battery vs Power Station — which backup type fits your use case
- How Long a CPAP Battery Lasts in a Power Outage — realistic outage runtime
- Best Solar Generator for CPAP — 2–4 kWh stations and solar bundles for multi-day outages
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