How Many Watts Does a CPAP Machine Use? (Real Numbers + Runtime Guide)
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CPAP machines do not use a lot of power.
So you might think almost any battery will work through the night.
That is exactly where most people get it wrong.
Quick Answer
| Setup | Typical Draw | Energy Per Night (8h) |
|---|---|---|
| CPAP without humidifier | 30 to 60W | 240 to 480Wh |
| CPAP with heated humidifier | 100 to 150W | 800 to 1200Wh |
| BiPAP without humidifier | 50 to 90W | 400 to 720Wh |
| BiPAP with heated humidifier | 120 to 180W | 960 to 1440Wh |
| Travel CPAP (DC mode) | 10 to 30W | 80 to 240Wh |
Low watts does not mean low energy needs. A CPAP runs 7 to 9 hours continuously. Use 80% of rated battery capacity as your real working number. The Top 5 LiFePO4 stations all handle overnight CPAP backup reliably.
The wattage of a CPAP machine is only one part of the equation. The number that actually determines whether your backup lasts the entire night is runtime, and runtime depends on factors that wattage alone does not reveal. Most buyers only discover this after their battery runs out at 3am during a real outage.
⚠️ The Misunderstanding
Seeing a low wattage number and concluding the battery requirement is also low. A CPAP drawing 50W sounds minimal. But running that load for 8 hours straight, accounting for inverter losses and battery protection cutoffs, requires more stored energy than most people calculate. Watts tell you how fast energy is consumed. They do not tell you how much energy you need for the full night.
What Affects CPAP Power Usage
The wattage of any given CPAP machine is not a fixed number. Several factors shift it meaningfully and every one of them affects how long your battery lasts.
Heated Humidifier
This is the single biggest variable in CPAP power consumption. A humidifier heating water to a comfortable temperature draws 60W to 100W on its own, on top of the machine's base motor draw. A CPAP running at 50W without humidification becomes a 130W to 150W load the moment the humidifier is active. That is a 2x to 3x increase in power demand and a corresponding reduction in battery runtime.
Pressure Settings
Higher pressure settings require the motor to work harder, which increases power draw. The difference between a low pressure prescription and a high pressure prescription can account for 10W to 20W of additional draw. Auto-adjusting machines (APAP) vary their pressure throughout the night, which produces variable power consumption that averages somewhere between the minimum and maximum pressure draw.
Machine Type and Model
Older CPAP models tend to draw more power than newer energy-efficient designs. BiPAP machines, which deliver two separate pressure levels for inhalation and exhalation, typically draw more than standard CPAP models. Travel CPAP machines are specifically designed for low power consumption and often draw significantly less than home models.
Real CPAP Power Numbers by Setup
| Setup | Typical Wattage | Wh Used Per Night (8 hrs) |
|---|---|---|
| CPAP, no humidifier, low pressure | 30 to 45W | 240 to 360Wh |
| CPAP, no humidifier, high pressure | 50 to 70W | 400 to 560Wh |
| CPAP, heated humidifier active | 100 to 150W | 800 to 1200Wh |
| BiPAP, no humidifier | 50 to 90W | 400 to 720Wh |
| BiPAP, heated humidifier active | 120 to 180W | 960 to 1440Wh |
| Travel CPAP (DC mode) | 10 to 30W | 80 to 240Wh |
Wh per night figures are raw energy consumed before efficiency losses. Add 25% to these figures to account for inverter conversion losses and battery protection cutoffs when selecting battery capacity.
Why Watts Are Not Enough: The Runtime Gap
Here is where most people's thinking goes wrong. They see a CPAP rated at 50W, look at a 500Wh battery, and calculate 10 hours of runtime. That math looks right. It is not.
Three factors reduce real-world runtime below the simple calculation:
Inverter efficiency losses. Converting stored DC battery energy to AC power through an inverter wastes roughly 10% to 15% of the stored energy. A 500Wh battery delivers approximately 425Wh to 450Wh of real AC output.
Battery protection cutoff. Most power stations stop discharging at 10% to 20% remaining charge to protect the battery from deep discharge damage. A 500Wh station that cuts off at 15% gives you approximately 425Wh before shutdown.
Combined effect. On a 500Wh station running a 50W CPAP, real usable runtime is approximately 500 x 0.80 / 50 = 8 hours. That is exactly enough for one night with no margin. If the machine draws 55W instead of 50W due to pressure variation, or if the humidifier activates briefly, that margin disappears.
The simple rule: always use 80% of rated battery capacity as your real working number when calculating runtime. Never plan to the theoretical maximum. For the complete runtime calculation framework, see our battery runtime guide and calculator (the same math applies to any continuous-draw device).
Note that **CPAP** backup is a pure runtime problem, not a startup surge problem. A **CPAP** motor draws steady, low wattage with no compressor spike. But if you are also protecting a refrigerator with the same station, the surge rating becomes critical for the fridge side of the equation.
Want to calculate exact runtime for your CPAP setup?
Use our free runtime calculator and enter your CPAP's wattage as the load value. Same formula, same accuracy.
Use the Runtime Calculator →What a Real Night Looks Like on Battery
You go to bed at 11pm. Your CPAP runs continuously until your alarm at 6:30am. That is 7.5 hours of uninterrupted operation. Your machine draws 55W at your prescribed pressure setting with humidifier off.
Energy consumed: 55W x 7.5 hours = 412.5Wh. Add the 25% efficiency factor: you need approximately 515Wh of rated battery capacity to cover this night comfortably. A 500Wh station cuts it very close. A 1000Wh station covers two nights without recharging. A 1024Wh station like the EcoFlow Delta 2 gives you full coverage with substantial margin.
Now run the same calculation with the heated humidifier active at 130W total draw: 130W x 7.5 hours = 975Wh. Adding the efficiency factor, you need approximately 1220Wh of rated capacity. A 1000Wh station falls short. A 1500Wh station covers it with margin. A 2048Wh station like the Bluetti AC200L covers two full humidified nights without recharging.
The Humidifier Mistake: Most Common Sizing Error
The majority of CPAP backup failures trace back to one thing: the buyer sized their battery for the machine's base wattage without accounting for the heated humidifier. The machine label shows 45W. The buyer buys a battery that handles 45W for 9 hours. The humidifier runs at 90W additional draw all night. The battery runs out by 3am.
The fix is simple. Find your machine's wattage with the humidifier active, not just the motor draw. Most manufacturers publish both figures in the product documentation or on the power adapter label. If you cannot find the humidifier-active figure, add 100W as a conservative estimate to your base motor draw and size accordingly.
For a full breakdown of how to size any backup station to your specific load, read our complete guide on what size power station you need (the sizing method applies identically to CPAP backup).
⚡ Modern Energy Tip
The easiest way to find your exact CPAP power draw is to check the input rating on the power adapter itself. It typically shows a maximum wattage or amperage figure. If it shows amps, multiply by 120 to convert to watts. This is the worst-case draw number. Actual consumption is usually lower, but sizing to the adapter rating gives you reliable margin for any operating condition.
What This Means for Choosing a Power Station
Once you know your real power draw including humidifier, the battery capacity decision becomes straightforward.
For a CPAP without humidifier drawing 50W, a 500Wh to 600Wh station covers a single night. A 1000Wh station covers two nights. For reliability with margin, a 1024Wh LiFePO4 station is the right single-station solution for most users.
For a CPAP with heated humidifier drawing 130W, a 1200Wh to 1500Wh station is the minimum for a single night with margin. A 1152Wh LiFePO4 station covers it tightly. A 2048Wh LiFePO4 station covers two full humidified nights without recharging.
The battery chemistry matters here as much as the capacity. LiFePO4 batteries handle continuous overnight discharge reliably and last thousands of cycles, which is exactly what CPAP backup demands. Standard lithium batteries degrade faster under repeated overnight use. Every station in our Top 5 tested lineup uses LiFePO4 chemistry with a pure sine wave inverter.
CPAP Backup Sizing Checklist
- Find your machine's wattage with humidifier active, not just motor draw
- Multiply by your actual sleep duration (typically 7 to 9 hours)
- Add 25% efficiency factor for inverter losses and battery cutoff
- Use 80% of rated capacity as your real working number
- Choose LiFePO4 battery chemistry for reliable overnight cycling
- Confirm pure sine wave inverter output (required for medical device compatibility)
- Always size for the worst-case scenario (humidifier on, high pressure, hot night)
- Test the full setup before storm season, not during an actual outage
Final Verdict
Watts Are the Starting Point. Runtime Is What Matters.
A CPAP machine's low wattage is reassuring but incomplete. The real question is how much total energy it consumes across a full night of therapy, and that number changes significantly depending on whether the heated humidifier is active. Size your backup battery for your actual setup, add a margin, and test before storm season.
The same LiFePO4 power stations that protect a refrigerator through extended outages are the right choice for CPAP backup. Pure sine wave output, overnight reliability, and thousands of charge cycles are what both applications require.
If this guide helped you, consider saving Modern Energy Guide in your bookmarks so you can quickly find the right information during your next power outage.