Backup Power for Medical Devices, Phones and Wi-Fi: A Family Sizing Worksheet
Medical devices come first. If someone in your home relies on powered medical equipment, talk with the doctor and device supplier about an outage plan, and ask your utility whether it has a medical-needs registry. Ready.gov has guidance for people with disabilities and medical needs (Ready.gov: Disabilities). This page is planning math, not medical advice.
Step 1: List loads (watts × hours = Wh)
| Device | Typical watts (check your label) | Hours | Wh |
|---|---|---|---|
| Router + modem | 15–25 W | 24 | 360–600 |
| Phones (4 charges) | ~15 Wh each | - | ~60 |
| CPAP without heated humidifier | 30–60 W | 8 | 240–480 |
| LED lamp | 8–10 W | 6 | ~60 |
These are example ranges. Use your device's label or manual.
Step 2: Add margin
Inverters lose energy. Plan on usable output being about 80–90% of rated capacity, and add a buffer. Our sister site has a free watt-hour calculator.
Step 3: Match a size class
- ~300–500 Wh: phones, Wi-Fi for part of a day, lights.
- ~1 kWh: Wi-Fi for a day, a CPAP night, phones, lights. Example: BLUETTI AC180 (affiliate link).
- ~2 kWh: adds a fridge for roughly a day. Examples: BLUETTI Elite 200 V2 (affiliate link), ALLPOWERS R2500 V2 class (affiliate link).
Look for a pure sine wave inverter and, if a device must not blink off, a UPS/pass-through mode with a fast switchover time listed in the manual. Runtime on paper is not a guarantee. Results vary with load, temperature, and battery age.