The “best CPAP UPS” is determined by energy, not marketing VA. A 1,000 VA computer UPS with a small internal battery may last less than a 500 W power station with a large watt-hour rating.
HHZ recommendations by outage pattern
| Situation | Best backup class |
|---|---|
| Brief cuts under 15–30 minutes | Pure-sine UPS with enough transfer/runtime |
| Occasional 6–8 hour outage | 500–1,000 Wh LiFePO₄ portable power station |
| Frequent nightly load-shedding | Pure-sine home inverter + dedicated 12 V 100 Ah or larger battery |
| Travel/camping | Device-approved DC battery or portable station, sized after a test |
| CPAP is medically critical with no interruption tolerance | Clinician/manufacturer-approved system plus a separate emergency plan |
Runtime math
Estimate:
Runtime hours ≈ usable battery Wh ÷ average device watts
A 500 Wh power station with 85% usable output provides about 425 Wh.
- At 40 W average: about 10.6 theoretical hours.
- At 80 W average: about 5.3 hours.
Actual runtime can be lower because pressure, leak, humidifier heat, tube heat, ambient temperature, inverter loss, and battery age change consumption. Measure the CPAP with a plug-in watt meter across a representative night.
Humidifier and heated tube are the swing loads
The blower itself is relatively efficient. Heated water and heated tubing can multiply total draw. If the patient tolerates it, battery mode with heated humidification reduced or disabled can turn a partial-night backup into a full-night backup.
Do not leave the humidifier chamber filled when the machine is moved. Spilled water can damage the blower.
Pure sine wave and electrical safety
Use pure-sine AC output unless the device manufacturer explicitly approves another waveform. Confirm voltage, frequency, earthing, maximum load, and the original power adapter.
A direct DC cable can avoid inverter losses, but it must be approved for the exact CPAP model and voltage. Never improvise polarity, connectors, or a higher-voltage cable.
What to buy
For most occasional-outage households, a LiFePO₄ power station around 500 Wh is the minimum useful starting point for a CPAP without heavy humidifier use; 700–1,000 Wh gives safer full-night margin with comfort features. Look for:
- Pure-sine output.
- Displayed watt and remaining-runtime data.
- Replaceable fuse/protection and documented warranty.
- Pass-through/UPS operation explicitly supported.
- LiFePO₄ chemistry for longer cycle life where available.
For frequent outages, a dedicated pure-sine inverter plus battery is usually cheaper per Wh. Keep CPAP on its own protected circuit so fans, lights, and phone charging do not silently consume the reserved capacity.
Test before relying on it
Run one complete night on backup at the actual prescription, mask, humidity, and tube settings. Record starting/ending battery, verify transfer behaviour, and repeat every few months. A backup that exists but has never been tested is not a clinical continuity plan.
Verdict
Buy by usable Wh and measured draw. A 500–1,000 Wh pure-sine LiFePO₄ station is the cleanest occasional-outage solution; a dedicated pure-sine inverter battery is better for regular cuts. Avoid small computer UPS units sold on VA alone.
Add the backup to the full CPAP starter-kit cost and recalculate runtime whenever the humidifier, heated tube, or device changes.