How big a portable power station do you actually need?
Sizing by wattage is the most common buying mistake. Wattage tells you what a unit can run at once; watt-hours tell you how long it can do it.
Start from a list, not a label
Write down what you want to run and for how long, then convert everything to watt-hours (Wh). Watts × hours = Wh.
| Load | Draw | Hours needed | Wh |
|---|---|---|---|
| LED lights (4) | 40W | 5 | 200 |
| Laptop | 60W | 6 | 360 |
| Phone charging | 15W | 6 | 90 |
| Fridge (see the duty-cycle note) | ~200W running | 24 at 40% duty | ~1,900 |
| CPAP without humidifier | 30-60W | 8 | 240-480 |
Add about 15% for inverter losses, then compare against the unit's rated Wh — and remember that many are quoted at the ideal discharge rate, which you will not get in the real world.
The fridge is always the deciding load
A modern fridge does not run continuously: a compressor cycles, typically 30-50% of the time depending on ambient and how often the door opens. So a fridge drawing 200W while running uses roughly 1.5-2.5 kWh per day, not 4.8. That is why a 1,000Wh unit can keep a fridge alive overnight, and why a 2,000Wh unit is the sensible outage choice. See running a fridge from a power station for the surge problem.
Surge is the number people forget
Anything with a motor or compressor pulls a startup surge of two to three times its running watts for a fraction of a second. A 200W fridge can demand 600W at startup. Check the unit's surge or peak rating, not only its continuous rating, or it will trip every time the compressor kicks in.
Choosing between two sizes
Rule of thumb for outages: buy for your worst realistic night, not your average. A unit that covers lights, phones, a laptop and a fridge for 12 hours typically means 1,000-1,500Wh for a short, managed outage, and 2,000Wh+ if you intend to run a fridge overnight without thinking about it.
And check recharge time, because it decides whether the unit survives a multi-day outage. A 1,500Wh unit that accepts 200W of solar needs 8+ hours of good sun; one that accepts 800W is a different tool entirely.
Where the marketing misleads
- "Runs a fridge for 24 hours" — usually a small bar fridge at ideal temperature, not a full-size unit in summer.
- Watt-hours quoted at 0.2C — gentle discharge that no real load replicates.
- Peak solar input — quoted for ideal sun and voltage; expect 60-75% of it in practice.
- Expansion batteries — often vendor-specific and priced far above equivalent capacity elsewhere.
Work the arithmetic for your own loads first, then buy the smallest unit that clears it. Calculator: battery runtime calculator.