Quick answer: A 500Wh power station runs a CPAP for about 36 hours on the machine alone, and under 7 hours with heated tubing and the humidifier at 8. ResMed’s own battery guide recommends 720 Wh for that eight-hour night — more than this tier holds.
This question has three defensible answers, and the pages that answer it pick one without saying which. The gap is not rounding: it is the difference between eight and a half hours and not enough for one night. What a CPAP draws at each setting is a separate article with ResMed’s own numbers in it; this one is about what a 500 Wh station does with them. For the wider decision, our power station sizing guide covers every tier.
Before anything else: a CPAP is prescribed medical equipment. Your pressure, your humidifier setting and whether either can change are questions for your clinician or equipment provider. Nothing below is treatment advice; it is arithmetic about watt-hours.
Three answers, all of them correct
Take the hardest case ResMed publishes: heated tubing at 30 °C with the humidifier at 8, which is 4.92 A at 12 V, or 59.0 W. Divide 500 Wh by that and you get eight and a half hours. Divide the 80 per cent that actually reaches a load and you get under seven. Ask ResMed and it tells you to buy 720 Wh. Same machine, same night.
| Which answer | Machine only, 11.2 W | Heated tube and humidifier, 59.0 W | What it assumes |
|---|---|---|---|
| Nameplate divided by watts | 45 hours | 8.5 hours | That every watt-hour reaches the machine |
| 80 per cent delivered | 36 hours | 6.8 hours | An inverter in the path, which is our planning figure |
| ResMed’s recommended battery | 144 Wh is enough | 720 Wh needed | Eight hours with a 50 per cent margin built in |
The third row is the only one written by the people who built the machine. 500 Wh is 69 per cent of what ResMed recommends for that configuration, and its margin exists so that a cold night or an ageing battery does not end the therapy early. Buying under it spends that margin before you start.
On the machine alone every answer agrees: a 500 Wh station covers several nights. The humidifier and the heated tube are 81 per cent of the load at the top setting. That is the whole spread of this article, and it is a setting, not a purchase — which is why it is a question for your provider and not for us.
The 1,000 W on the box is not a surge rating
ResMed asks for something specific when a humidifier is in use: a pure sine wave inverter of 300 W continuous and 500 W peak. So the sensible next step is to check a 500 Wh station against that, and the headline figures look generous. EcoFlow publishes 512 Wh with 500 W of AC output and 1,000 W of X-Boost for its RIVER 2 Max.
That second number is not a surge rating. In EcoFlow’s own words, “X-Boost reduces the voltage of your appliances so you can power them with a lower-rated inverter”, and the same page warns that “the change of voltage may affect device usage performance”. Every appliance EcoFlow lists as an example is a heater, a kettle, a hair dryer or a drill. A pure sine wave at reduced voltage is not the mains, and ResMed asked for the mains.
Read the continuous figure instead and the answer is easy: 500 W of pure sine output clears ResMed’s 300 W and 500 W comfortably. The inverter is not what limits this tier, any more than the surge rating limits a sump pump. The capacity is.
One real gate is a device question, not a station question: ResMed’s guide names heated humidifiers that must not be used with an inverter at all. If your machine is an older one, that page decides the matter before any arithmetic does.
Which is why the 12 V socket matters more than the battery
Run the machine from the station’s 12 V output through the manufacturer’s DC converter and the inverter leaves the path. That is where the 80 per cent goes, and why rows one and two differ. A 500 Wh unit’s car port is rated around 120 W against the 59 W this load asks for at its worst.
ResMed prefers that route and gives four reasons of its own: efficiency, protection against reversed leads, regulation as the battery voltage falls, and an automatic cut-out at 10.5 V so the battery is not flattened. On a night when the difference is six and a half hours against eight, the socket you plug into is worth more than the next size up.
How we calculated this
The watt figures are ResMed’s published amps at 12 V multiplied by 12, from this site’s own verified record. Runtimes are a nominal 500 Wh times 0.8 divided by those watts; the 0.8 is our planning figure, taken from the runtimes one manufacturer publishes for its own product, and it is what separates row one from row two. Real units in this class hold 512 to 518 Wh.
ResMed’s recommended sizes are given in amp-hours at 12 V — 12 Ah machine only, 60 Ah for heated tube and humidifier at 8 — and converted here at 12 V. Its 50 per cent margin is already inside them, which is why they sit above the bare arithmetic rather than beside it. No product was tested by us and none is recommended. Our method is described at how we test.
This page is about electricity, not treatment
A CPAP is prescribed medical equipment. We have deliberately not suggested turning anything off to save power. Humidification settings, pressure and whether either can change are decisions for your clinician or equipment provider, and they should size backup power with you rather than from a table.
Ask your electricity network operator about its medical or priority-restoration register, which exists for exactly this. And do not wire a station into your home’s circuits or feed a house through a wall socket — that is backfeeding and it can kill line workers.
Frequently asked questions
Will a 500Wh power station run a CPAP all night?
On the machine alone, several nights over. With heated tubing and the humidifier at its top setting, our arithmetic gives 6.8 hours, and ResMed’s own recommendation for an eight-hour night is 720 Wh, which this tier does not reach; that is a question for the next size up. What yours is set to is not ours to say.
Why do other sites give a longer figure?
Two reasons. They divide the nameplate rather than the delivered capacity, and they assume a wattage — 30 W, 40 W, 52 W are all in circulation — instead of reading ResMed’s published table, where the same machine spans 11.2 to 59.0 W depending on configuration. Neither habit is dishonest; both make the answer longer.
Does the 1,000 W rating help?
Not for this. On a 500 Wh station that figure is usually X-Boost, which EcoFlow describes as reducing the voltage so a smaller inverter can cope. The specification that matters here is the 500 W of continuous pure sine output, and it already clears what ResMed asks for.
Is DC really better than the AC socket?
It removes the conversion that costs the 20 per cent, and ResMed gives four reasons of its own for preferring a DC converter. A 500 Wh station’s car port is rated around 120 W against a 59 W load, so headroom is not the issue. Use the converter the manufacturer specifies, not a generic lead.
The short version
A 500Wh power station is generous for the machine and short for the humidifier, and the manufacturer says so more plainly than any runtime chart: 720 Wh for an eight-hour night at the top setting. Check your own configuration against ResMed’s table rather than an assumed wattage, use the 12 V socket if your machine and its converter allow it, and take the sizing conversation to the people who prescribed the machine.
This article is general information, not an installation guide and not a substitute for a licensed electrician. Electrical work on a service panel, a transfer switch or a utility connection is regulated in most jurisdictions and normally requires a permit and an inspection. Fuel-burning equipment produces carbon monoxide and must never be run indoors, in a garage or near an opening into the home.
