Heating changes everything
Turning off optional humidity or heated tubing can extend runtime, but only change therapy settings if your clinician and device instructions allow it.
Medical-device power planning
CPAP Battery Backup Runtime Calculator
Estimate how long a battery can run your CPAP after accounting for humidifier use, AC or DC conversion losses, battery health, reserve capacity, and other loads.
AC + DC efficiencyBattery agingTreatment-night estimateUncertainty range
Why CPAP battery estimates often miss
A battery’s printed watt-hours are not the energy that reaches the machine. Charge level, cell aging, the reserve you choose to keep, and conversion losses all reduce usable output. Humidifiers and heated tubing can then raise the CPAP’s average demand substantially.
DC is often more efficient
A manufacturer-approved DC cable can avoid AC inverter losses. Confirm voltage, polarity, connector, and compatibility before use.
Measure your real load
Pressure, mask leak, climate, heater setting, and machine model affect demand. A power meter gives a better input than a generic preset.
The formula used
Runtime hours = [Battery Wh × start charge × battery health × (1 − reserve) × conversion efficiency] ÷ (CPAP watts + other loads)
The calculator also shows a planning range using ±20% load variation. That range is not a guarantee; cold temperatures, battery-management cutoffs, or a worn pack can reduce real runtime further.
Typical planning watts
| Setup | Planning draw | What changes it |
|---|---|---|
| Travel CPAP, no heating | 20 W | Pressure, leaks, model |
| Full-size CPAP, no heating | 30 W | Pressure and comfort features |
| CPAP with humidifier | 60 W | Humidity level and room conditions |
| Humidifier + heated tube | 80 W | Tube temperature and climate |
Before relying on a battery overnight
- Read the CPAP and battery manufacturers’ power and compatibility instructions.
- Measure actual consumption for a normal night with your usual accessories.
- Test the complete setup before travel or a predicted outage.
- Keep a conservative reserve and a separate contingency plan.
- Never use a fuel-burning generator indoors or in an enclosed space.
Important: This calculator is an electrical planning estimate, not medical advice or a guarantee of therapy time. Do not change prescribed pressure or treatment settings based on this tool. Discuss medical questions with your clinician and confirm backup-power requirements with the device manufacturer.
CPAP battery runtime FAQ
How many watt-hours do I need for one CPAP night?
Multiply measured average watts by treatment hours, then divide by the expected conversion efficiency and usable battery fraction. For example, a 60 W setup for eight hours needs 480 Wh delivered before accounting for reserve and conversion losses.
Does a humidifier shorten CPAP battery runtime?
Usually, yes. Water heating and heated tubing can be a large share of total power use. Measure your own device because settings and climate change the average load.
Is DC better than an AC outlet?
A compatible DC connection is often more efficient because it avoids the battery’s AC inverter. Use only an approved cable with the correct electrical specifications.
Can I use the battery’s advertised Wh directly?
No. Starting charge, battery health, reserve, conversion loss, temperature, and battery-management cutoffs all affect energy delivered to the CPAP.
Learn the assumptions behind these inputs in how many watts does a CPAP use? Related tools: battery backup time calculator, power station runtime calculator, and the appliance wattage library.