CPAP battery backup calculator
For a medical device used indoors, only a battery (optionally recharged by solar) is safe. Enter your devices, hours of use and nights of backup to get the battery capacity in watt-hours.
Updated
1. Pick your appliances
Choose how many of each appliance you want to run and how many hours a day they run. Wattages are typical values: check the label on your own appliances.
CPAP machine (no humidifier)
60 W running · 60 W starting
0 / 2CPAP heated humidifier
50 W running · 50 W starting
0 / 2Home oxygen concentrator
350 W running · 700 W starting
0 / 1Phone / tablet charger
20 W running · 20 W starting
0 / 10
2. Your result
We add up the running watts, then add the single largest starting surge (motors never all start at the same second).
Recommended battery
—
Add at least one appliance to see your result.
- Running watts
- 0 W
- Starting peak
- 0 W
- Energy used per day
- 0 Wh
Power source
Locked to “Solar / battery”: never run a fuel-burning generator indoors (carbon monoxide).
Frequently asked questions
Why not use a generator for a CPAP or oxygen concentrator?
Engines produce carbon monoxide, an odorless gas that the CDC links to more than 400 deaths in the US each year. A generator must never run inside the home or garage, which is where medical devices are used. A battery produces no emissions.
Does turning off the humidifier make a difference?
Yes, often a big one. The heated humidifier can use as much power as the CPAP itself, or more. Running without it roughly halves the battery you need for the same number of nights.
Does this replace advice from my doctor or equipment supplier?
No. Wattages are typical values. Check the real power draw in your device's manual and ask your home medical equipment supplier, especially for life-sustaining equipment.
Why are starting watts higher than running watts?
Anything with a motor or compressor (fridge, AC, pumps) draws 2 to 3 times its running watts for a second or two when it starts. The calculator adds the single largest surge, because in practice motors don't all kick on at the same moment.
Why add a 20% safety margin?
A generator or inverter running at 100% all the time runs hot, wears faster and trips on the smallest surge. Aiming for about 80% of rated output leaves room for a forgotten appliance or a real draw higher than the label.
What's the difference between watts (W) and watt-hours (Wh)?
Watts measure power at a given moment: they size the generator or inverter. Watt-hours measure energy over time: they size the battery. A 60 W CPAP used for 8 hours uses 480 Wh.