Wh vs W, explained
Watt-hours are the tank; watts are the tap — you need enough of both, and they answer completely different questions.
Every power-station spec sheet leads with two numbers that look similar and mean opposite things. Get them straight once and the rest of the sheet reads itself.
Watt-hours: the size of the tank
A watt-hour is one watt of power drawn for one hour. It measures a quantity of energy — how much the battery holds — so it decides how long the station can keep going.
Think of it exactly like the fuel tank in a car. A 1,000Wh station can, in principle, deliver 1,000 watts for one hour, 100 watts for ten hours, or 10 watts for a hundred hours. Same tank, different burn rate. The bigger the Wh number, the longer you last — and the more it weighs and costs, because watt-hours are literally cells of lithium.
The catch: no station delivers its label. The battery holds back a protection reserve, and turning stored DC into household AC costs roughly 15% in inverter losses. That’s why we count real usable watt-hours, not the number on the box — a “1,000Wh” unit realistically serves about 765Wh to an AC device.
Watts: the size of the tap
A watt is a rate — power flowing right now. On a power station, the watts rating is the inverter’s ceiling: the most it can deliver at any instant. It decides what you can plug in, not how long it lasts.
If the tank is watt-hours, watts are how wide you can open the tap. A station rated for 1,000W continuous can run anything that draws up to 1,000W at once — a coffee maker, a few laptops, a small fridge. Plug in a 1,500W hair dryer and it doesn’t matter that the battery is full: the tap can’t flow that fast, so the unit trips to protect itself.
This is the number buyers most often overlook. Capacity gets the marketing; the inverter’s continuous watts quietly decide whether the station is useful for your actual appliances.
The two numbers, side by side
Watts answer “can I run it?” Watt-hours answer “for how long?” A complete sizing decision needs both, plus the surge rating for anything with a motor.
| Watts (W) | Watt-hours (Wh) | |
|---|---|---|
| What it is | A rate — power flowing now | A quantity — energy stored |
| Analogy | Width of the tap | Size of the tank |
| Set by | The inverter | The battery cells |
| Answers | Can I plug this in? | How long will it run? |
| If it's too small | The device won't start (trips) | It starts, but dies early |
A quick worked example: a 60W CPAP-style load on a 1,000Wh station. The watts question passes easily — 60W is well under any inverter’s ceiling. The watt-hours question sets the runtime: ~765 usable Wh ÷ 60W ≈ 12–13 hours, or about a night and a half.
Don't forget surge watts
Motors and compressors spike to two–six times their running watts for a split second at startup. Stations publish a separate, higher surge rating for that moment — and if your device’s spike beats it, the unit shuts off even though the running watts fit.
A fridge that hums along at 180W can jump past 1,000W the instant its compressor kicks in. Space heaters and hair dryers are steady loads (no surge) but high continuous watts; fridges, pumps, and power tools are the opposite — modest to run, brutal to start. Our sizing tool checks the worst single-start moment against each station’s sourced surge spec, and flags any station whose surge rating we can’t verify rather than guessing.
Frequently asked questions
- What is the difference between Wh and W on a power station?
- Watt-hours (Wh) are the size of the tank — the total energy stored, which sets how long the station runs. Watts (W) are the size of the tap — how much power it can push out at once, which sets what you can plug in. A station can have plenty of watt-hours but too few watts to start a big appliance, or a huge inverter but a small battery that empties fast.
- How do I calculate how long a power station will run my device?
- Roughly: battery-side usable watt-hours × output efficiency ÷ the device's watts = hours of runtime. A 1,000Wh-class station running a 100W TV lasts about 10 hours in theory. After roughly 15% AC conversion loss, plan on closer to 8–8.5 hours. BatteryRank also shows the resulting AC-delivered estimate explicitly.
- How many watt-hours do I need?
- Add up each device's watts × the hours you'll run it, then add about 15% for inverter losses. A CPAP without heated humidification is only ~9W for 8 hours (~80Wh a night); a full-size fridge averages ~1,260Wh a day at the wall. Your total daily watt-hours, times the number of days you need to cover, is your target capacity.
- Why can't I run my microwave even though the battery is full?
- Because that's a watts problem, not a watt-hours problem. A 1,000W microwave needs an inverter that can continuously deliver at least 1,000W (and briefly more at startup). If the station's continuous output is only 600W, it trips instantly no matter how full the battery is. Check the running-watts and surge-watts numbers, not just capacity.
- What are surge or starting watts?
- Motors and compressors — fridges, pumps, power tools — briefly pull two to six times their running watts at the instant they start. A fridge that runs at 180W can spike past 1,000W for a fraction of a second. A station has a separate, higher surge rating for that moment; if the surge exceeds it, the unit shuts off even though the running watts fit.