How Many Watt-Hours Do You Actually Need?
The most expensive mistake in portable power is buying more capacity than you'll use. The second most expensive? Not buying enough. Here's how to get it right.
Every portable power station review tells you the capacity in watt-hours. But most people have no idea what a watt-hour actually means in practical terms. "1,024Wh" — is that a lot? Enough for a weekend? A week?
It depends entirely on what you're running. So let's figure it out.
The basic formula
Watt-hours = Watts × Hours
A 60W laptop running for 4 hours uses 240Wh. A 5W phone charger running for 3 hours uses 15Wh. Add up all your devices and you know your daily usage.
But there's a catch: you lose about 10-15% of stored energy to inverter inefficiency. A 1,000Wh power station delivers about 850-900Wh of usable power to your AC devices. USB and DC outputs are more efficient (5-8% loss).
Rule of thumb: Multiply your calculated usage by 1.2 to account for inefficiency and a safety margin. Don't drain your battery to 0% regularly — it reduces lifespan.
Common device power consumption
| Device | Watts | Typical Use | Daily Wh |
|---|---|---|---|
| Smartphone charge | 5-10W | 2 hrs | 15Wh |
| Laptop (work use) | 50-80W | 6 hrs | 420Wh |
| LED camping lantern | 5-10W | 5 hrs | 40Wh |
| 12V fridge (car-style) | 40-60W avg | 24 hrs | 1,200Wh |
| CPAP machine | 30-60W | 8 hrs | 360Wh |
| Portable fan | 20-40W | 8 hrs | 240Wh |
| Wi-Fi router | 10-15W | 24 hrs | 300Wh |
| Induction cooktop | 1,000-1,800W | 0.5 hrs | 700Wh |
| Electric blanket | 40-80W | 8 hrs | 480Wh |
| Full-size fridge | 100-200W avg | 24 hrs | 3,000Wh |
Scenario calculations
Weekend camping (2 nights)
Recommendation: 256-300Wh class (EcoFlow River 2, Jackery Explorer 300 Plus)
Van life (daily)
Recommendation: 2,000-2,500Wh class (EcoFlow Delta 2 Max, Bluetti AC200L) + 200-400W solar panel for daily top-up
Home outage backup (24 hrs)
Recommendation: 4,000-5,000Wh class (EcoFlow Delta Pro 3, or Bluetti AC200L + B300)
Two things most people get wrong
1. Confusing watts with watt-hours. A power station's watt (W) rating tells you how much it can output at once — like how wide a pipe is. The watt-hour (Wh) rating tells you how much total energy it stores — like how big the tank is. A 300W station with 1,000Wh can run a 300W device for about 3 hours. A 2,000W station with 1,000Wh can run more demanding devices, but for less time.
2. Ignoring standby draw. Your power station uses 5-15W just being turned on, even with nothing plugged in. Over 24 hours, that's 120-360Wh of phantom drain. Turn it off when you're not actively using it. Most modern units have an auto-shutoff feature — use it.
The practical advice
Buy 20-30% more capacity than your calculation suggests. You'll always find something extra to plug in. And it's much cheaper to buy the right size once than to upgrade later.
That said, bigger isn't always better. A 5,000Wh station that you only use 1,000Wh of is just dead weight you're paying for. Match the station to the use case.
Ready to buy? Check our 2026 buying guide organized by use case. Need a solar panel to pair with it? See our solar panel guide.