Running a CPAP machine on a power station: 12V vs AC, humidifier and nights per charge

Plan on roughly 530Wh of battery per 8-hour night if you run a ResMed AirSense 11 with its humidifier on, from the station's AC outlet. That means a 1,024Wh station covers about two nights, and a small 286Wh one won't get you through one. Turn the humidifier off and plug in through ResMed's 12V DC converter and the same battery lasts several nights.

The machine figures here come from ResMed's Australian user guide and shop, the station specs from EcoFlow's Australian pages, and the outage advice from Energex and Energy Made Easy. All are linked at the bottom. We haven't measured any of this ourselves; the runtimes are sums, and the working is shown.

What a CPAP actually draws

ResMed's AirSense 11 user guide lists a typical power consumption of 56.1W and a peak of 73.2W, from a 65W power supply that puts out 24V. ResMed doesn't say which settings the typical figure assumes, but the system it describes includes the HumidAir tub and the heated ClimateLineAir tube, and ResMed says humidifiers use a substantial amount of power. The blower on its own uses less. ResMed doesn't publish a figure for that, and it changes with your pressure setting.

So use 56.1W as your planning number with the humidifier on, and find your own number with it off. Most power stations show the watts going out on their screen. Run the CPAP from the station for an hour on a normal evening, at your usual pressure, and write down what the display settles on.

If you've got a different machine, the same figures are in the specifications section at the back of its user guide. Look for "typical power consumption".

Nights per charge, worked out

The sum is the battery's watt-hours, times 0.85 for inverter and conversion losses, divided by the CPAP's watts. That gives hours. Divide by 8 for nights.

Take the EcoFlow DELTA 3 Plus at 1,024Wh with the humidifier on. That's 1,024 x 0.85 = 870Wh usable, and 870 / 56.1 = about 15.5 hours, or just under two nights. For the second column below we've used 20W as an example of a machine with the humidifier and heated tube off. It isn't a ResMed figure, so swap in the number you read off your own station.

Those are rough. The 0.85 is a general allowance for the AC route, and a hot, humid Queensland night pushes the heated tube harder than a mild one. If anything else shares the station, like a fan or the modem, add its watts to the CPAP's before you divide. Our runtime calculator does the adding up for you.

Turn the humidifier off on battery

ResMed's own advice is that humidifiers use a substantial amount of power, and that you should consider turning the humidifier off or detaching it when you're running from a battery or DC converter. Going by the numbers above, that's the biggest single change you can make. A dry night is uncomfortable, but it's a lot better than the machine stopping at 3am.

If you find you can't sleep without humidity, talk to your sleep physician or equipment supplier about a lower setting before storm season, rather than working it out in the dark.

12V converter or the AC outlet

There are two ways to plug in. The simple one is the CPAP's normal power supply into one of the station's AC outlets. It works, but the station turns its battery's DC into 230V AC, then the CPAP's power brick turns it back into 24V DC, and you lose some energy at each step.

The other is ResMed's AirSense 11 DC/DC Converter, which ResMed says runs the machine from a 12V or 24V DC outlet. On a power station that's the 12V car-style socket. The RIVER 3 Plus, for example, has one rated at 12.6V and 10A (126W), which is plenty for a 73.2W peak. Skipping the inverter usually stretches the battery further, though the converter has losses of its own and ResMed doesn't publish an efficiency figure.

The DC/DC converter is model-specific. The AirSense 11 version suits the AirSense 11 and AirCurve 11 range; older machines have their own converters, so check the accessories list in your user guide before you buy one. ResMed also advises against running a CPAP from your car's starting battery for long, because car batteries aren't designed to be drained deeply.

Setting it up beside the bed

Charge the station during the day, while you're home and awake, and unplug it once it's full. The Queensland Fire Department says not to leave lithium-ion batteries charging unattended, to charge them on a hard surface away from bedding, curtains and carpet, and not to use one that's hot, swollen or damaged. That rules out leaving a station on charge all night next to the bed as your outage plan, even though some stations offer a UPS mode that switches over in under 10 milliseconds.

So the plan is a full station sitting on a tiled or hard floor near the bed, with air around it. When the power goes, move the CPAP's lead (or the DC converter) across to the station. Do a test night before you need it.

Register as a life support customer

Energex lists a "chronic positive airways pressure respirator" among the equipment that makes you eligible for its Life Support Program. You register by calling Energex on 1300 659 869 or through your electricity retailer, and your doctor signs a medical confirmation form.

Registration means you're told about planned outages before they happen. Energex is clear that it doesn't guarantee supply or put you first for restoration after a storm. Energy Made Easy suggests a written plan as well: who you'll call, where you'll go if the battery runs low and the power isn't back, and how you'll get there with the machine. Our blackout and cyclone season guide covers the rest of the house, and if you travel with your CPAP, the caravan and camper sizing guide has a worked example with one in the van.

Where to buy in Australia

Buying from the brand's Australian store means 230V AU outlets, the local warranty and local support. Prices move around a lot, so check on the day.

• EcoFlow RIVER 3 Plus (286Wh, expandable to 858Wh)EcoFlow AustraliaSee it at EcoFlow Australia
• EcoFlow DELTA 3 Plus (1,024Wh, 1,800W)EcoFlow AustraliaSee it at EcoFlow Australia