Watt-hours (Wh) are the size of the tank. Watts (W) are the size of the pipe. Sales pages shout the pipe because 2000 W looks like 2000 Wh. It is not.
hours = (battery Wh × usable fraction × inverter efficiency) / load watts
Use 0.85–0.90 for AC inverter efficiency unless the manual gives a better number. Use 0.9 as a usable fraction if you do not want to flatten LFP to 0% every outage. For 12 V loads, drop the inverter term.Step 1 — nameplate watts
Read the sticker. A “120 W” laptop brick is a maximum, not a cruise number. A fridge sticker is often start watts plus running watts in fine print. If the sticker is missing, a $20 plug-in watt meter is more scientific than a blog table. We will not publish a fake appliance encyclopedia.
Step 2 — hours
An 8-hour evening is not a 48-hour ice storm. Write the duration first. Then multiply. Then add 20% because you will forget the Wi-Fi closet and the phone chargers.
Step 3 — match the inverter
If the load is 1400 W, a 800 W rated station is the wrong object, even if the watt-hours are huge. Surge ratings (Jackery 2000 v2: 4400 W surge; DELTA 2: 2700 W surge) are for short motor starts, not for running a 3000 W heater. Manufacturer boost modes (X-Boost, Power Lifting) have footnotes. Read them.
Step 4 — pick a class
| Need (very rough) | Wh class | Example SKUs on this site (mfr. Wh) |
|---|---|---|
| Phones, CPAP math, LEDs | 250–300 Wh | RIVER 2 256 Wh; Explorer 300 Plus 288 Wh |
| Camp cooler, small outage | 500–800 Wh | Explorer 500 v2 512 Wh; RIVER 2 Pro 768 Wh |
| Fridge evening + router | ~1 kWh | 1000 v2 1070; DELTA 2/3 1024; AC180 1152 |
| Overnight fridge + morning | ~2 kWh | Explorer 2000 v2 2042; DELTA 2 + extra 2048 |
| Multi-day essentials | 4 kWh+ | DELTA Pro 3 4096; DELTA 3 expanded; or gas hybrid |
Worked example: mini-fridge + Wi-Fi + lights. CPAP-only arithmetic: CPAP Wh math (not medical advice).
Sources
SKU watt-hours from manufacturer pages listed in README.md, checked 9 September 2026. Efficiency 0.85 is a planning factor, not a lab result.