How many hours a power station runs the devices you need in an outage.

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How we calculate

By Sam Hollis, editor · Updated Oct 4, 2026

We calculate every hour figure on this site; nobody ran a CPAP to get them. This page shows the math, the defaults we use when a figure is missing, and where each capacity number comes from.

The formula

Hours = usable energy (Wh) ÷ (device watts + the power station's idle draw).

Usable energy is what a tester got out of the unit, which is less than the rated figure on the box. Idle draw is the power the station uses to run its own inverter.

A worked example

The Anker SOLIX C1000 Gen 2 is rated at 1,024Wh. An independent test drew 890Wh from it (Jul 23, 2026). Anker doesn't publish an idle figure for it, so we use 12W. The AirSense 11's typical draw is 56.1W.

890 ÷ (56.1 + 12) = 13.1 hours. At the 73.2W peak: 890 ÷ (73.2 + 12) = 10.4 hours.

Defaults when a figure is missing

  • No independent test: rated capacity × 0.85. The 11 measured units in this table delivered 78 to 93% of their rating, with a middle value of 86%, so 0.85 is a fair stand-in. These rows are marked "Estimate" and drawn as outlined blocks.
  • No maker idle figure: 12W. The 3 units here with a maker figure (2 Bluetti, 1 Anker) list 9 to 15W.

Checking the math against a real test

One of the tests we use ran its units at about 34W and got 49 to 63% of their rated capacity out. For the Bluetti AC180, our formula with that test's 980Wh measurement and its 14W idle reading gives 60%, inside that range (59% with Bluetti's own 15W figure, which the table uses). Low loads lose a bigger share to idle draw, and the formula catches that.

Where the measurements come from

  • OutdoorGearLab: DELTA Pro 3, Explorer 1000 v2, Explorer 2000 v2, C1000 Gen 2; latest test Jul 23, 2026
  • Outdoor Life: AC180, Explorer 1000 Plus, FlashSpeed 1500; latest test Jan 9, 2026
  • StorageReview: DELTA 3 Plus, DELTA 2 Max, F3800; latest test Jan 2, 2025
  • Trusted Reviews: Elite 200 V2; latest test Mar 27, 2025

Download the data

Outage Hours CPAP table (CSV): model, rated Wh, usable Wh, source, tester, test date, idle W, hours at typical and peak draw, stock check date. Free to use with credit (CC BY 4.0 for the calculated columns).