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“How long will it last?” is the first question every CPAP user asks about a battery — and it’s the one most product pages dodge. The honest answer depends on two things: the size of the battery and whether you run the heated humidifier. Once you understand the math, you can predict runtime for any machine and any power station within a few minutes. I’ve been researching power stations with sleep apnea gear for years, and in this guide I’ll hand you the exact formula, real runtime tables, and the settings that quietly drain your battery faster than you’d expect.

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🧮 Skip the math: our free CPAP Battery Runtime Calculator does it for you — pick your pressure, humidifier, and battery size for an instant nights-of-runtime estimate.

The Formula That Answers Everything

Runtime comes down to one equation:

Runtime (hours) ≈ (Battery Wh × 0.85) ÷ CPAP watts

The 0.85 is inverter efficiency. Any power station that converts its DC battery to AC (the standard wall-plug approach) loses roughly 10–15% of its stored energy as heat during the conversion. So an advertised 500Wh battery really delivers about 425Wh to your machine through the AC outlet.

The second number you need is your CPAP’s actual draw:

• Without heated humidifier: ~10–15 watts. I use 12W as a safe average.
• With heated humidifier + heated tube: ~40–60 watts. I use 50W for planning.

That’s it. Plug in your numbers and you have your answer.

A Worked Example (500Wh Station)

Let’s run a common mid-size 500Wh power station through the formula so you can see how it works.

Humidifier OFF, 12W draw:

(500 × 0.85) ÷ 12 = ~35 hours of runtime. At 8 hours per night, that’s roughly 4 nights on a single charge.

Humidifier ON, 50W draw:

(500 × 0.85) ÷ 50 = ~8.5 hours — barely 1 full night.

Read that again, because it’s the single most important takeaway on this page: turning on the heated humidifier cuts your runtime by 75% or more. The same 500Wh battery that lasts four nights dry lasts one night humidified. Everything else is a rounding error compared to this one setting.

Runtime Table: Nights by Battery Size

Here’s the practical version. I’ve run the formula for every common power station capacity, at 8 hours per night, using 12W (dry) and 50W (humidified). I’ve rounded down to whole nights because you never want to bet your therapy on a battery limping to 6%.

Battery Capacity	Usable Wh (×0.85)	Nights (no humidifier, 12W)	Nights (with humidifier, 50W)
100Wh	~85Wh	~1	Less than 1
300Wh	~255Wh	~2–3	~1
500Wh	~425Wh	~4	~1
768Wh	~653Wh	~5–6	~1–2
1,000Wh	~850Wh	~7–8	~2
1,500Wh	~1,275Wh	~11–13	~2–3

Notice how the humidifier column barely moves as capacity climbs. To get multiple humidified nights, you need serious capacity — 1,000Wh or more. That’s why my standing advice for CPAP users is simple: if you can sleep comfortably with the humidifier off, do it. You’ll get four to six times the runtime out of the same battery.

What Actually Drains Your Battery Faster

The table above assumes typical conditions. Several real-world factors will shorten those numbers, so plan with a margin.

1. The Humidifier (by far the biggest)

Covered above, but it bears repeating because nothing else comes close. Heated humidification is a comfort feature, not a medical necessity for most users. On battery nights, switch it off and use a CPAP HME heat-and-moisture exchanger instead — a small inline filter that recycles your own exhaled moisture. It costs a few dollars, needs zero power, and keeps your airway from drying out.

2. High Pressure Settings

The motor works harder at higher pressures. If your prescription runs at 14–20 cm H₂O, expect draw at the top of the range (closer to 15W dry). Auto-adjusting machines that spend the night ramping up and down also pull a bit more than a fixed low setting.

3. Heated Tubing

Even with the humidifier tank off, a heated hose can add 10–20W on its own. If your machine lets you disable the heated tube independently, do it on battery nights.

4. Cold Temperatures

Lithium batteries hate the cold. Near freezing, a power station can temporarily lose 20–30% of its usable capacity. If you’re camping in winter, keep the unit inside your sleeping area or an insulated bag, not out in the vestibule. See my notes in the winter camping power guide if this is your use case.

5. AC Inverter Loss (and how to beat it)

That 0.85 efficiency factor is avoidable. Many CPAPs — including most ResMed and Philips units — can run directly off a 12V DC output with the right cable, skipping the AC inverter entirely. Going DC-direct typically recovers 10–15% of your runtime and runs cooler and quieter. Check your machine’s manual for a DC input port and its required voltage before buying a cable. This one trick can turn a marginal 4-night battery into a comfortable 5-night one.

Recommended Power Stations for CPAP Runtime

Here are the units I actually recommend, matched to how many nights you need. All runtimes assume the humidifier is off.

Product	Capacity	Weight	Nights (no humidifier)	Best For
EcoFlow River 3	245Wh	7.8 lbs	~2	Ultralight weekend trips
Bluetti EB3A	268Wh	10.1 lbs	~2	Budget 2-night backup
Jackery Explorer 300 Plus	288Wh	8.3 lbs	~2	Compact travel
Jackery Explorer 600 Plus	632Wh	13.1 lbs	~4–5	Lightweight multi-night
EcoFlow RIVER 2 Pro	768Wh	17.2 lbs	~5–6	Best all-around pick
Bluetti AC180	1,152Wh	35 lbs	~8–9	Long outages / humidifier users

If you want one recommendation for most people, it’s still the EcoFlow RIVER 2 Pro. It hits the sweet spot: nearly a week of dry runtime, a fast 220W solar input for recharging off-grid, and a weight you can still lift into a car. For a full head-to-head of the options, see my best battery backup for CPAP roundup.

How to Recharge for Continuous Use

Runtime tables assume you’re starting full. For outages lasting more than a few nights, or for extended camping, you’ll want to top the battery back up:

• Solar: A 100–220W panel recharges most CPAP-sized stations in 4–8 hours of good sun. This is what makes portable power stations superior to sealed CPAP batteries for off-grid use.
• Car: A 12V car outlet trickle-charges slowly but reliably during a daytime drive.
• Wall: When grid power returns intermittently, even an hour on the wall buys you another night.

Pairing your station with solar effectively gives you unlimited nights as long as the sun shows up. That’s the whole reason I steer CPAP campers toward power stations over dedicated batteries.

Frequently Asked Questions

How many watt-hours does a CPAP use per night?

With the humidifier off, a typical CPAP uses about 80–120Wh over an 8-hour night (roughly 12W × 8 hours). With the heated humidifier and tube on, that climbs to 320–480Wh — three to five times more.

Can a power station run a CPAP all night?

Yes, easily. Even a small 245–300Wh unit runs a humidifier-off CPAP for a full night with power to spare. The question is how many nights, which depends on capacity — see the runtime table above.

Should I use AC or DC to power my CPAP?

DC-direct if your machine supports it. Running off the 12V DC port skips the inverter and recovers 10–15% of your runtime, while running quieter and cooler. Check your CPAP manual for a DC input and the correct voltage before buying a cable.

How do I get more nights out of my battery?

Turn off the heated humidifier and use an HME filter, disable heated tubing, run DC-direct instead of AC, and keep the battery warm in cold weather. Doing all four can roughly double your usable nights.

Will a power station run a ResMed AirSense 11?

Yes. The AirSense 11 draws about 10–12W without humidification, so it follows the same math in this guide. I cover machine-specific cable and DC details in the ResMed AirSense 11 battery guide.

Do I need to worry about the inverter turning off?

Some small stations have an “eco mode” that shuts the AC outlet off when draw is low — and a 12W CPAP can trip it. Disable eco/auto-off mode on the AC output before you go to sleep, or run DC-direct to avoid the issue entirely.

You Might Also Like

• Power Stations for CPAP: The Complete Guide — our master resource for every CPAP power scenario.
• Best Battery Backup for CPAP, Tested — the units I actually recommend and why.
• How to Size a Portable Power Station — the full watt-hour sizing walkthrough.
• How Long Does a Portable Power Station Last? — runtime math for every appliance, not just CPAP.
• Best Battery Backup for the ResMed AirSense 11 — machine-specific picks and cables.

Final Thoughts

Predicting CPAP runtime isn’t guesswork once you have the formula: (Battery Wh × 0.85) ÷ CPAP watts. Memorize it and you can size any battery for any machine in thirty seconds. The single decision that matters most is the humidifier — leaving it off and using an HME filter can stretch a battery from one night to four or five. From there, DC-direct wiring, disabling heated tubing, and keeping the unit warm in the cold squeeze out the rest.

For most CPAP users, a 768Wh station like the EcoFlow RIVER 2 Pro hits the ideal balance of nights, weight, and solar recharging. Buy for the way you’ll actually sleep — humidifier on or off — add a night of margin, and you’ll never wake up to a dead battery and untreated apnea.