How we test

Some power-draw figures on this site are still provisional estimates rather than our own meter readings. Pages carry a note where that is the case. We are working through the machines in order of how often they come up.

Measuring draw

Every runtime figure here starts from one number: how many watts a machine actually pulls. We measure it with an inline meter at a stated pressure, with the humidifier off and then at a mid setting, because the humidifier is a heating element and changes the answer by roughly five times. Where heated tubing is fitted we say so.

Calculating runtime

Runtime is capacity divided by draw, minus two losses people usually forget: cells are not drained to zero, so we count 90% of rated capacity as usable, and AC inversion costs roughly 10–15%, so we apply 85% efficiency on AC and 95% on DC. Those constants live in a single file and every page derives from them, which means no two pages here can quote contradictory numbers.

What we don't do

CPAP Power Lab covers electricity and equipment. We do not advise on pressure settings, mask prescriptions, whether you need therapy, or whether snoring means you have sleep apnoea. Those are questions for a clinician and a sleep study, and getting them wrong matters more than any battery decision. If a page ever strays into that territory, it is a bug — tell us.

Money

We earn affiliate commission on some links. It does not change a runtime figure — the maths is the maths, and it is shown so you can check it.