Disclosure: This page contains affiliate links. Last updated: 21 September 2026. Planning math, not a lab certificate. How we review.
Watt-hours vs watts is the confusion that sells the wrong box. The carton prints a big watt-hour number. The compressor asks for watts. They are not interchangeable.
Full method: Size the Load.
Watts (W) — can it start and run?
Watts measure power right now.
- Running watts: what the appliance draws while it is on.
- Surge / peak watts: the short spike when a motor starts.
If the station’s continuous watts sit below running watts, the inverter trips. If surge sits below compressor start, the refrigerator never turns on. That problem is documented on Refrigerator.
A CPAP is the opposite shape: low watts, long hours. CPAP.
Watt-hours (Wh) — how long?
Watt-hours measure energy in the battery.
Rough idea: 100 W for 10 hours = 1,000 Wh of load.
Sticker watt-hours are not hours of runtime. Inverters waste heat. This site plans with about 85% usable unless a named test says otherwise.
Runtime hours ≈ (sticker Wh × 0.85) ÷ average watts
Average watts ≈ running watts × duty cycle. A fridge compressor is often on 30–40% of the day. A CPAP is close to continuous for 6–8 hours.
One kitchen, both numbers
Top-freezer ~150 W running, ~600 W surge, 35% duty.
- Watts test: station needs enough continuous and surge to start that compressor.
- Watt-hours test: 150 × 0.35 × 24 = 1,260 Wh/day of load → about 1,480 Wh sticker for a full day after 85%.
A “1,000 Wh / 300 W” travel station fails the watts test on that fridge even if the Wh number looks friendly. A “1,000 Wh / 1,800 W” station can pass watts and still fail a two-day storm on energy.
How to read a spec sheet
| Label on the box | Unit | Question it answers |
|---|---|---|
| Output / rated / continuous | W | Can it keep the load on? |
| Surge / peak / starting | W | Can it start a motor? |
| Capacity | Wh | How long, after 85%? |
| Solar input | W | Recharge speed in sun — not extra capacity at 2 a.m. |
Ignore lifestyle photos until these four are clear.
FAQ
No. One is power. One is energy.
Neither. Match watts to the appliance, then watt-hours to the hours. Size the Load.
Those charts assume a load you may not have. We republish runtime only with watts, hours, and the usable factor.
Method: How we review.
Installed vs portable: Portable vs installed battery.
Contact: Contact.
Disclosure: Affiliate disclosure.