Runtime
9.56hours
Estimated runtime after efficiency and reserve.
CPAP Battery Backup Calculator
Estimate CPAP battery runtime in hours and nights from battery capacity, power draw, humidifier use, efficiency, and reserve.
This is a power estimation tool, not medical advice. It can help compare energy assumptions, but critical medical equipment backup plans should be checked with the device manufacturer, clinician, or qualified professional.
CPAP battery inputs
Wh
Use battery or power station capacity in watt-hours.
W
Use the device or power supply wattage when available.
hours
Nightly use duration for the nights estimate.
Humidifier heat can materially increase power draw.
%
Estimated conversion efficiency when using AC output.
%
Energy kept unused for planning margin.
This is a power estimation tool only, not medical advice. Critical equipment backup planning should be checked with the device manufacturer, clinician, or qualified professional.
Results
Estimated nights
1.2nights
Based on 8 hours per night.
Adjusted CPAP load
40W
Humidifier impact
+0W
Usable battery energy
383Wh
Calculation breakdown
| Item | Value | Notes |
|---|---|---|
| Base CPAP load | 40 W | Entered power draw before humidifier adjustment. |
| Humidifier mode | off | 0 W added for the selected mode. |
| Adjusted load | 40 W | Base CPAP watts plus humidifier estimate. |
| Usable battery energy | 383 Wh | 85% efficiency and 10% reserve applied. |
| Runtime | 9.56 hours | 383 Wh / 40 W adjusted load. |
| Medical notice | Power estimate only | This is a power estimate only and is not medical advice for critical equipment backup planning. |
Formula
runtimeHours = capacityWh x (efficiencyPercent / 100) x (1 - reservePercent / 100) / (cpapWatts + humidifierExtraWatts)The calculator adds the humidifier estimate to the CPAP load, reduces battery capacity by efficiency and reserve, then divides usable watt-hours by adjusted watts. Estimated nights are runtime hours divided by hours per night.
- capacityWh
- Battery or power station capacity in watt-hours.
- cpapWatts
- Base CPAP power draw in watts.
- humidifierExtraWatts
- Estimated added load: off 0 W, low 20 W, high 40 W.
- hoursPerNight
- Runtime hours are divided by this value to estimate nights.
Example
Turning on a heated humidifier can add a meaningful load and reduce the runtime estimate.
- Battery capacity is 500 Wh.
- CPAP power draw is 40 W with humidifier off, so adjusted load is 40 W.
- With 85% efficiency and 10% reserve, usable energy is 382.5 Wh.
- 382.5 Wh divided by 40 W gives about 9.56 hours.
- At 8 hours per night, that is about 1.2 estimated nights.
How to use this calculator
- Enter battery capacity in watt-hours.
- Enter CPAP power draw from the device, power supply, or manual.
- Select humidifier mode and enter the expected hours per night.
- Review the runtime, estimated nights, warnings, and medical equipment notice.
Input guide
- Battery capacity: stored energy before losses and reserve.
- CPAP power draw: base watts for the machine before humidifier adjustment.
- Hours per night: nightly use assumption for the estimated nights result.
- Humidifier mode: estimated extra load for heated humidification.
- Efficiency and reserve: planning assumptions for conversion loss and unused battery margin.
Common mistakes
- Forgetting that humidifier heat can reduce battery runtime.
- Assuming the estimate guarantees a full night of operation.
- Using an accessory or power supply number that does not match the actual setup.
- Treating a power estimate as medical advice or emergency planning approval.
Limitations
The estimate uses simple watt-hour arithmetic and fixed humidifier adders. It does not model pressure settings, mask leaks, ramp behavior, heated hose settings, DC adapter losses, battery age, temperature, altitude, or manufacturer reserve behavior.
FAQ
How does humidifier use affect runtime?
Heated humidifiers can add a meaningful load, reducing runtime compared with CPAP-only operation.
Does this guarantee a full night of CPAP use?
No. It estimates energy use from assumptions. Battery condition, pressure settings, accessories, and device behavior can change runtime.
Is this medical advice?
No. This is only a power estimation calculator. Backup plans for medical equipment should be reviewed with the device manufacturer, clinician, or qualified professional.
Should I use AC or DC power for CPAP backup?
Use the method supported by your equipment and battery. DC adapters may reduce conversion losses for some setups, but follow the manufacturer guidance for the device and battery.
Related calculators
Compare CPAP battery needs with power station runtime, UPS runtime, and outage planning tools.
- Portable Power Station Runtime CalculatorEstimate how long a portable power station can run a load after efficiency losses and reserve.
- UPS Runtime CalculatorEstimate UPS runtime for routers, computers, NAS devices, and other small electronics.
- Home Outage Backup PlannerPlan 24, 48, or 72 hour backup needs for critical home loads using battery and generator estimates.
Methodology and disclaimer
This is a power estimation tool, not medical advice. For critical medical equipment backup planning, consult the device manufacturer, clinician, or qualified professional.
The calculator adds an estimated humidifier load to the entered CPAP watts, applies inverter efficiency and battery reserve, then divides usable watt-hours by adjusted watts and hours per night.