The single most expensive mistake power station buyers make is buying on the wrong number. The big number on the box — “2000W!” — tells you almost nothing about how long it lasts. Here’s the five-minute version of getting this right.
Watts vs watt-hours
- Watts (W) = how much power a device draws right now. Think: speed.
- Watt-hours (Wh) = how much total energy the battery stores. Think: tank size.
A 60W CPAP running 8 hours needs 480Wh. A 1,500W space heater running 1 hour needs 1,500Wh. Same battery, wildly different runtimes.
The sizing formula
Wh needed = (device watts × hours of use) ÷ 0.85
The 0.85 is inverter loss — converting the battery’s DC to wall-style AC costs about 15%. If you can run the device from the station’s 12V DC port instead (common for CPAPs and car fridges), use 0.95 instead.
Then add 25–50% headroom for cold weather, battery aging, and the devices you forgot.
Worked example: an outage evening
| Device | Watts | Hours | Wh |
|---|---|---|---|
| Refrigerator (cycling) | 60 avg | 12 | 720 |
| Router + modem | 15 | 12 | 180 |
| 3 LED lights | 30 | 5 | 150 |
| 2 phones + laptop | 60 | 2 | 120 |
| Total | 1,170 Wh |
1,170 ÷ 0.85 ≈ 1,375Wh — so a 1,500–2,000Wh unit covers a comfortable outage evening with margin. That’s why our home backup picks cluster around 2,000Wh.
Two numbers that trip people up
- Surge/peak rating: compressors (fridges, AC units, pumps) draw 3–7× their running watts for a split second at startup. Your station’s surge rating must clear that. Any unit rated 1,000W+ continuous handles a fridge.
- Recharge speed: a big battery that takes 12 hours to recharge is a liability in rolling outages. Look at wall-charge time — modern LiFePO4 units range from under an hour to 2+ hours for a full charge.
Where to go next
- Sizing for a fridge and essentials: Best portable power stations for home backup
- Sizing for sleep apnea machines: Best power stations for CPAP
- Choosing between the big four brands: EcoFlow vs Jackery vs Bluetti vs Anker
Frequently asked questions
What's the difference between watts and watt-hours?
Watts measure how fast power flows right now; watt-hours measure the total energy stored. A 60W device running for 10 hours uses 600Wh. Your power station's Wh rating is the tank size, its W rating is how big the tap is.
Why does my power station die faster than the math says?
Three reasons: inverter conversion loses 10–15%, batteries deliver less in the cold, and capacity fades with age. Always size with a 25–50% safety margin.