The highest-value pair of loads in most houses. You do not need a Powerwall for this. You do need honest watts.
Call it 0.25–0.40 kW average for CPAP + fridge + internet if you turn the humidifier down. A 3.84 kWh F3800 Plus 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. Fridge, CPAP, and internet are also the first night of what dies first in a multi-day outage.
Read the brick, not the box. Many CPAP machines run from an external power supply that turns 120 V AC into DC, often 24 V and sometimes 12 V. The label on that brick, or the nameplate on the machine, gives the input volts, output volts, and watts. Plugging the original brick into the battery’s 120 V AC outlet is the simple path. A DC cable to the battery’s 12 V port is only for an adapter your CPAP maker or supplier lists for your exact model. Do not match a DC cable from a photo. If the label and the port do not agree, stay on AC.
The CPAP is gentle. The fridge compressor is not. Each start pulls a short surge that can be several times its running watts, so read the fridge nameplate or manual for the real number. The battery’s continuous rating has to cover everything running at once (fridge, CPAP, router), and its surge rating has to cover the fridge starting on top of that. The watts above are planning ranges; your nameplate wins.
Rated watt-hours are not usable watt-hours. Inverter losses and the battery’s reserve take a cut. This page plans at 92% × 95%, about 87% of the label, and a cold room or a heated humidifier takes more. Divide the derated kWh by your average kW, not your peak. Run your own loads in the runtime calculator. If night two matters, add the same-brand extra battery before you buy a second box.
If someone in the house depends on an oxygen concentrator or other life-support equipment that runs continuously, a battery is a bridge, not the whole answer. That equipment can draw far more than a CPAP, and running the battery flat is not an acceptable way for the plan to fail. Talk to your doctor or equipment supplier about backup supply and the batteries the device maker supports. Enroll in your utility’s medical-needs program (often called medical baseline or critical care) before the next outage, and know where you will go if the power stays out. This page covers the CPAP-and-fridge case only.
1 kWh / 1.8 kW. Enough for CPAP + fridge + router if you buy the extra pack for night two.
2.05 kWh, 2.4 kW, 41.7 lb. Skip it if a well pump is also on the list.
Overkill on watts for CPAP. The reason to start here is a well, a 240 V tool, or extra batteries in the same family.
This job does not need 6 kW. DELTA 3 or C2000 Gen 2 covers it; F3800 Plus is the step up if you also want 240 V. Buy the extra battery before you buy a second brand. For a multi-day fuel-vs-battery choice, see generator vs battery vs hybrid.
View DELTA 3 on EcoFlow View C2000 Gen 2 on Anker View F3800 Plus on Anker Find my backup Checklist 2026 rankings Generator vs battery