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The right CPAP power-station size is not a universal 300Wh, 500Wh, or 1000Wh answer. It is the labeled capacity needed to deliver the energy used by your machine, therapy settings, humidifier, heated tube, output cable, and sleep schedule, with room left for conversion losses and reserve.

This page is a purchase-planning guide, not medical advice and not a promise of medical backup reliability. If interruption of therapy creates a serious health risk, ask your clinician or equipment provider what contingency plan is appropriate before relying on any consumer power station.

Use the strongest number you can get

Use these inputs in this order:

  1. A full-night watt-hour measurement: This captures cycling heaters and changing pressure better than a single instant watt reading. Use only a measurement method permitted by the device instructions and your equipment provider.
  2. The manufacturer’s battery table: Match the exact machine, treatment pressure, humidifier, heated tubing, and connection method. ResMed’s battery guide, for example, provides different current and battery figures for different AirSense 10 configurations and includes a stated safety margin in its tables.
  3. A documented average watt figure: Use a value for the complete setup, not merely the blower and not the maximum rating printed on the power brick.

Heated accessories can materially change the result. In ResMed’s own AirSense 10 table, the current and eight-hour battery recommendation change when the humidifier or ClimateLine tubing is added. That is evidence that the settings must be part of the calculation, not a reason to copy one ResMed number to another machine.

Do not change prescribed therapy settings just to make a battery last longer unless your clinician or equipment provider says that is appropriate.

Calculate labeled watt-hours, not just one night’s load

First find the delivered energy:

nightly energy (Wh) = measured average watts x hours of use
trip or outage energy (Wh) = nightly energy x nights before recharge

Then allow for the power path and the reserve you intend to keep:

minimum labeled capacity (Wh) = trip energy / (delivery efficiency x planned usable fraction)

Here is a hypothetical example, not a CPAP default:

  • Measured average draw: 35W
  • Use: 8 hours per night for 2 nights
  • Delivered energy: 35 x 8 x 2 = 560Wh
  • AC delivery efficiency assumption: 85%, or 0.85
  • Planned usable fraction after 20% reserve: 80%, or 0.80
  • Minimum labeled capacity: 560 / (0.85 x 0.80) = 824Wh

An 824Wh requirement means a 768Wh unit is undersized under those assumptions. Compare models above the calculated requirement; do not round down to the nearest marketing class.

The CPAP power station runtime calculator performs this planning math. If you only need to answer whether an existing unit can cover tonight, use the shorter overnight CPAP feasibility check.

Capacity and output are separate checks

Watt-hours answer how much energy is stored. They do not prove that the station can operate the machine. Before buying, verify all of the following against the CPAP and power-station manuals:

  • The complete CPAP setup’s continuous power requirement is below the station’s output limit.
  • The connector, voltage, polarity, and cable are explicitly compatible.
  • Any DC cable is approved for the exact CPAP model; a plug that physically fits is not enough.
  • The AC waveform or inverter requirements in the device documentation are met.
  • The station can remain on at a low overnight load without an automatic shutoff ending the session.
  • Fan noise, display brightness, alarms, and charging lights are acceptable at the bedside.

A DC connection can avoid the station’s AC inverter, but it is not automatically more suitable. Use it only when the machine manufacturer identifies a compatible converter or cable.

Plan recharge and failure response before shopping

A battery sized for one night is not a two-night plan unless it can be recharged in time. Write down the wall-charge time, vehicle-charge limits, solar input range, and the realistic charging source available during the outage. Solar nameplate watts are not guaranteed delivered watts, so use the solar recharge time calculator to test conservative input rather than assuming perfect sun.

The FDA advises people who use powered home medical devices to read the instructions, understand backup options, keep emergency contacts, and have a plan for a power outage. A calculator cannot provide that operational plan. The CPAP outage backup checklist covers the cable, rehearsal, contact, and recharge details that capacity math misses.

Compare candidates only after the calculation

Treat those as candidate lists, not proof of compatibility. Verify the exact model number on the manufacturer page, read both manuals, and confirm the return policy before purchase.

Next action: record one normal night’s energy use or locate the exact manufacturer battery table, enter that value in the CPAP calculator, and reject every model whose capacity or output falls below the result.