Picking a power station looks complicated because of all the specs on the box, but it really comes down to two numbers. Get them wrong and one of two things happens: you spend a lot on a 100-pound unit you never come close to emptying, or you buy one that cuts out the second your fridge compressor kicks on.
I size them in three steps.
Step 1: Decide what actually has to stay on
Think about the outage, not your normal day. For most homes the list is short:
- The refrigerator, and maybe a chest freezer
- Phones, the Wi-Fi router and modem, a laptop
- A few LED bulbs or lanterns
- Medical gear like a CPAP, an oxygen concentrator or a medication fridge
- A sump pump if you have a basement, or a well pump if you’re on a well
Cross off anything that makes heat. Space heaters, hair dryers, kettles and electric ovens pull 1,000–1,800 W each and can empty a battery in under an hour. A propane camp stove costs a fraction of the battery capacity it saves you.
Step 2: Add up the watt-hours
For each item, multiply its watts by the hours you’ll use it in a day. The result is in watt-hours (Wh), which is how power station capacity is measured.
| Appliance | Watts | Hours/day | Wh/day |
|---|---|---|---|
| Refrigerator (cycling) | 180 | 8 | 1,440 |
| Wi-Fi router + modem | 20 | 24 | 480 |
| 3 LED bulbs | 30 | 6 | 180 |
| Phones (×2) | 30 | 2 | 60 |
| Laptop | 60 | 4 | 240 |
| Total | 2,400 |
Then divide by 0.85. Power stations lose 10–15% turning battery power into 120 V AC, and the box never mentions it.
2,400 Wh ÷ 0.85 ≈ 2,820 Wh for one full day
That’s what you’d need to get through 24 hours without recharging. If you can top up from solar or your car every day, you can go smaller.
Step 3: Check output and surge
Capacity is the size of the tank. Output is the size of the engine, and it’s the spec most people skip.
- Continuous output: add the running watts of everything that might be on at the same time. Here that’s 180 + 20 + 30 + 30 + 60 = 320 W, which almost any unit can handle.
- Surge: motors need a quick spike to start. A fridge compressor can pull around 1,200 W for a split second, so the surge rating has to cover your running load plus that jump, roughly 320 + 1,020 ≈ 1,340 W.
If you want to run a microwave (about 1,500 W from the wall), a window AC or a sump pump, look at output carefully. That’s where the cheap units fall short.
Turning your number into a size
| Your daily need | Size to look for | Typical weight |
|---|---|---|
| Under 500 Wh (phones, CPAP, router) | 250–500 Wh | 7–15 lb |
| 500–1,000 Wh | 1,000 Wh | 22–35 lb |
| 1,000–2,500 Wh (fridge + essentials) | 2,000–3,000 Wh | 45–70 lb |
| 2,500 Wh+ or 240 V needs | 3,600 Wh+ expandable | 90 lb+ |
Three mistakes I see a lot
- Believing the runtime on the box. Manufacturers divide capacity by watts and stop there. On AC power, real runtime is about 15% lower.
- Ignoring the battery type. Go with LiFePO4 (LFP). It’s rated for 3,000+ cycles, compared with roughly 500–800 for older NMC cells, and it’s more thermally stable.
- Forgetting about recharging. A big battery only helps if you can refill it. Check how fast it charges from the wall (one to two hours is common now) and how much solar it accepts.
Quick reference
- Phones, router and a CPAP: 300–500 Wh is plenty.
- A fridge for a day plus the basics: 2,000–3,000 Wh, with at least 1,800 W of output.
- Multi-day outages, pumps or AC: an expandable 3,600 Wh+ system, ideally with solar, or a generator.
If you’d rather skip the arithmetic, put your own appliances into the power station size calculator and it runs all three steps for you.