The humidifier decides everything
Champion's published wattage chart puts a CPAP at 30–60 watts. Over an eight-hour night that is roughly 240–480Wh — a genuinely small load that a modest battery covers.
A heated humidifier is a different thing. It is a heating element, and heating elements are among the largest loads in any house per unit of size. Manufacturers do not generally publish a combined figure, but the practical effect is that total consumption can double or triple.
So the first question is not which battery. It is: do you use heated humidity, and can you go without it for a few nights? If you can, the purchase gets much smaller and cheaper. That is a question for your clinician, not for us.
| Setup | Draw | Per 8-hour night |
|---|
| CPAP, humidifier off | 30–60 W (published) | ~240–480 Wh |
|---|
| CPAP with heated humidifier | Substantially higher | Often 2–3× the above |
|---|
| CPAP on DC input, no humidifier | Lower again — no inverter losses | Check your machine's DC rating |
|---|
The 30–60W figure is Champion Power Equipment's published range. The humidifier multiplier is a working characterization rather than a published number — we have not measured any machine, and your device's own label is the figure that counts.
Three things that change your real number
- Pressure setting. Higher prescribed pressure means the blower works harder and draws more.
- Altitude compensation. Machines that adjust for altitude run the blower faster to hold pressure.
- Mask leak. A leaking seal makes the machine compensate continuously, which costs power all night.
None of these are large individually. Together they are why you should buy some margin rather than sizing exactly to a calculation.
Use the DC input if your machine has one
Many CPAP machines accept 12V DC directly, and most power stations have a 12V output. Going DC-to-DC skips the station's inverter, and inverter conversion is a real loss — commonly in the region of 10–15%.
On a load this small that is meaningful: it can be the difference between one night and one night with margin, from the same battery, for the cost of a cable. Check your machine's manual for the DC input specification and use the manufacturer's own cable rather than a generic one.
Why recharge speed beats capacity here
This is the argument this page exists to make. Most outages are short, and power often returns intermittently before it returns for good.
A battery that refills in an hour turns every brief restoration into a full reset. A battery with twice the capacity but a six-hour recharge does not — it can arrive at the second night still half empty.
For a nightly medical load with a predictable daily cycle, fast recharge is worth more than raw watt-hours. The charging options cover AC, solar and car charging.
Test it before you need it
Plug your actual machine into the actual battery and run it for a full night. Two things get discovered this way and only this way:
- What your device really draws, at your pressure, with your mask, with your humidifier setting.
- Whether the station's inverter idles down. Some stations power off an AC outlet that appears to be drawing nothing, which is a problem for a device that cycles.
Do it on an ordinary Tuesday. Discovering either of those at 3am in a storm is the situation the equipment was bought to prevent.
If the outage might run days
A battery alone has a ceiling. For multi-day coverage you want a recharge path — a folding panel, or a generator running outdoors in blocks to refill the battery that runs the bedroom.
The battery indoors is not optional in that arrangement: it is the only thing that can safely sit beside a sleeping person. Backup power for medical devices covers oxygen concentrators and refrigerated medication, which are much larger problems than a CPAP.
