How long does a CPAP battery take to recharge?

From a wall outlet, a 292Wh station refills in about 1 hour at 300W and a 1,024Wh station in under 4 hours. From a car's 12V socket the same units take about 2.7 and 9.5 hours. From a 100W solar panel, about 3.2 and 11.4 hours of good sun.

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EcoFlow Delta 3
Fastest wall refill
High-wattage AC input is what makes a 1,024Wh unit practical mid-outage — under 4 hours at 300W, and well under an hour on fast charge, instead of an overnight wait.
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Power-draw figures for the machines below are provisional estimates, not yet our own meter readings. See how we test.

Recharge time is capacity divided by input power, plus about 10% for charging losses. The reason answers vary so wildly is that the three methods differ by more than an order of magnitude in what they can push.

The arithmetic

hours = capacity ÷ (input watts × 0.9)

The 0.9 covers heat lost in charging. Most stations also taper the last 10-20% to protect the cells, so the final stretch takes longer than the formula suggests — treat the result as the time to roughly 90%.

Recharge time by method

For the two most common capacities:

Hours to refill from empty
Method	Input	292Wh	1,024Wh
Wall, fast charge	1,200W	0.3 h	0.9 h
Wall, standard	600W	0.5 h	1.9 h
Wall, slow/trickle	300W	1.1 h	3.8 h
Car 12V socket	120W (10A)	2.7 h	9.5 h
Car 12V socket	96W (8A)	3.4 h	11.9 h
Solar, 100W panel	100W	3.2 h	11.4 h
Solar, 200W panel	200W	1.6 h	5.7 h
Solar, 400W panel	400W	0.8 h	2.8 h

Assumes 90% charging efficiency. Solar figures assume peak output, which real panels reach only in clear midday sun — see the note below.

Why the solar numbers are optimistic

A 100W panel does not make 100W all day. It makes close to that for a few hours around solar noon and much less either side. The honest unit is peak sun hours — typically 3 to 5 a day depending on latitude and season.

A 100W panel at 4 peak sun hours puts in roughly 400Wh of raw output, or about 300Wh after charging losses. That is one dry night's use (64Wh) several times over, but barely one humidified night (320Wh).

You usually do not need a full charge

The useful question is rarely "how long to full" but "how long to cover tonight". Dry therapy costs about 65Wh. On a 100W panel that is around 45 minutes of good sun. Humidified costs about 320Wh, or roughly 3.5 hours.

That asymmetry is why the humidifier decision dominates recharging as much as it dominates runtime.

Can I charge a CPAP battery while using it?: Most power stations support pass-through, powering the machine while charging. Check your unit's manual — some disable AC output while fast-charging, and pass-through on a small CPAP battery is not universal.
How long does a 1,000Wh power station take to charge from a car?: About 9.5 hours from a 10A 12V socket, or 11.9 hours at 8A. Many cars cut power to the socket when the ignition is off, so check before relying on an overnight charge.
Is fast charging bad for the battery?: Repeated fast charging generates more heat and, over many cycles, shortens life — which is why most units default to a slower rate. LiFePO4 cells tolerate it better than NMC.

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