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 | 50–80 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 | ~9 W typical | 40–65 W | 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 is significantly more efficient than the AirSense 10, using a 65 W adapter versus the older 90 W unit. The AirMini is the most battery-friendly option at just 6–7 W typical draw. For detailed wattage breakdowns, see our CPAP power consumption guide.
Runtime by battery size and CPAP model (at 10 cmH2O)
This table shows usable runtime hours at a common 10 cmH2O pressure, assuming DC-direct for dedicated CPAP batteries and a 20% AC inverter loss for power stations. Values are rounded to the nearest half hour.
| Battery (Wh) | AirMini (7 W) | AirSense 11 no hum. (10 W) | AirSense 11 + hum. (48 W) | AirSense 10 + hum. (55 W) | BiPAP + hum. (70 W) |
|---|---|---|---|---|---|
| 100 Wh (Jackery 100 Plus) | 14 hrs | 10 hrs | 2 hrs | 1.5 hrs | 1 hr |
| 150 Wh (NiteOwl) | 21 hrs | 15 hrs | 3 hrs | 2.5 hrs | 2 hrs |
| 241 Wh (Jackery 240 v2) | 27 hrs | 19 hrs | 4 hrs | 3.5 hrs | 2.5 hrs |
| 266 Wh (Renogy / EASYLONGER) | 30 hrs | 21 hrs | 4.5 hrs | 4 hrs | 3 hrs |
| 297 Wh (Bluetti X30 / Yeti 300) | 42 hrs | 29 hrs | 5 hrs | 4.5 hrs | 3.5 hrs |
| 384 Wh (SUPA LiFePO4) | 43 hrs | 30 hrs | 6.5 hrs | 5.5 hrs | 4.5 hrs |
| 518 Wh (Jackery 500) | 59 hrs | 41 hrs | 8.5 hrs | 7.5 hrs | 6 hrs |
| 576 Wh (DARAN LiFePO4) | 65 hrs | 46 hrs | 9.5 hrs | 8.5 hrs | 6.5 hrs |
| 614 Wh (Bluetti X60) | 87 hrs | 61 hrs | 10.5 hrs | 9 hrs | 7 hrs |
| 1024 Wh (EcoFlow DELTA 2) | 117 hrs | 82 hrs | 17 hrs | 15 hrs | 12 hrs |
The bottom line: If you run a humidifier, you need at least 500 Wh for a full 8-hour night. Without a humidifier, 200–300 Wh covers most ResMed and Philips machines. 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)
- 35 W × 8 hrs = 280 Wh (AirSense 11 low humidifier)
- 48 W × 8 hrs = 384 Wh (AirSense 11 with heated tube, level 4)
- 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.
- Measured draw: 48 W (AirSense 11 at 10 cmH2O, humidifier level 4, heated tube on, verified with a Kill-A-Watt meter)
- Target runtime: 8 hours
- Raw Wh: 48 × 8 = 384 Wh
- Inverter buffer (AC power station): 384 × 1.20 = 461 Wh minimum
- Cold-weather buffer (camping at 40°F): 461 × 1.15 = 530 Wh
- Match to catalog: The Jackery Explorer 500 (518 Wh) is borderline; a 576 Wh DARAN LiFePO4 or 614 Wh Bluetti X60 gives comfortable margin.
If you drop the humidifier and use DC-direct instead, the same machine needs just 10 W × 8 hrs × 1.10 = 88 Wh — a 6x difference. 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) | +10% | Minimal conversion loss; some cable resistance |
| AC power station (pure sine inverter) | +20% | Inverter idle draw + 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, SUPA 384Wh, DARAN 576Wh, Bluetti AC60/AC200L) 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: 280 Wh × 1.20 = 336 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, Freedom V² View on Amazon, Zopec Explore Mini View on Amazon) |
| 100–250 Wh | Small power station or dedicated CPAP battery (Bluetti X30 View on Amazon, Jackery 240 v2 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 2 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.
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 15–40 W; use an HME filter instead
- Turn off the heated tube — saves 10–25 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 (10% for DC): 176 × 1.10 = 194 Wh
- Recommendation: Jackery Explorer 240 v2 (241 Wh) — one full night with room to spare
With humidifier on (level 4):
- Power draw: ~48 W
- Wh needed: 48 × 8 = 384 Wh
- Buffer (20% for AC): 384 × 1.20 = 461 Wh
- Recommendation: Jackery Explorer 500 (518 Wh) — one full night with humidifier
What about multi-night trips?
Multiply your single-night Wh by the number of nights. For a 3-night camping trip at 194 Wh/night (DC-direct, no humidifier), you need about 582 Wh.
Options:
- One large battery: EcoFlow DELTA 2 (1,024 Wh) handles 5+ nights
- Battery + solar panel: A 100 W panel recharges ~300 Wh during a sunny day
- Two smaller batteries: Bring two Jackery 240s 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
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