Battery backup for a CPAP and a refrigerator
The highest-value pair of loads in most houses. You do not need a Powerwall for this. You do need honest watts.
Planning watts (running, typical)
- Modern CPAP without a heated humidifier: often 30–60 W. Heated hose/humidifier can exceed 100 W. Use your machine’s label.
- Fridge: nameplate 100–200 W running, but it cycles. A planning average of 150 W is common. Chest freezer similar or lower.
- Router + ONT: 15–25 W.
Call it 0.25–0.40 kW average for CPAP + fridge + internet if you turn the humidifier down. A 3.84 kWh F3800 at 92% × 95% usable is about 3.36 kWh → ~8–13 hours at that load, more if the fridge is efficient and you keep the door shut. A 12 kWh Ultra X is measured in days at this load.
Use the calculator in appliance mode. Do not trust “runs a CPAP for a week” marketing unless they state humidifier off and the exact Wh.
This job does not need 6 kW. DELTA 3 or C2000 Gen 2 covers it; F3800 is the step up if you also want 240 V. Buy the extra battery before you buy a second brand.
DELTA 3 C2000 Gen 2 F3800