Guide
The single most common mistake in buying a portable power station is looking at only one number. Sizing correctly means solving for two separate things at once: how much energy you need stored, and how much power you need delivered at any instant. Get both right and your station quietly does its job; get either wrong and you'll be disappointed. Here's the straightforward method.
Watt-hours (Wh) measure the size of the battery — the total amount of work it can do. For each device, multiply its running watts × the hours you'll run it, then add them all up. A 60W mini fridge for 10 hours is 600Wh; add a 60W laptop for 4 hours (240Wh) and you're at 840Wh of actual work.
You can't use every watt-hour on the label. Convert your raw total by roughly +15% for inverter inefficiency (turning battery DC into household AC) and +20% so you're not draining the battery to empty, which shortens its life. So 840Wh of work means shopping for about 840 × 1.15 × 1.25 ≈ 1,200Wh of rated capacity.
Capacity isn't enough — the station's continuous output watts must exceed the total running watts of everything you'd power at once. And anything with a motor or compressor (fridges, pumps, tools) briefly pulls a startup surge of several times its running watts, so the station's surge rating must clear that spike or it will shut off despite a full battery.
| Capacity | Good for |
|---|---|
| ~300Wh | Phones, laptops, CPAP, lights — day trips |
| ~500–600Wh | CPAP overnight, mini fridge, weekend camping |
| ~1000Wh | Full fridge, power tools, short home backup |
| ~2000Wh | Full-day outage, RV, multiple appliances |
| 3000Wh+ | Off-grid, expandable, high-output loads |
Say you want to power a mini fridge, charge two phones and a laptop, and run a few LED lights for a two-day trip. Estimate each load with the Department of Energy's method — wattage × hours, from its Estimating Appliance Energy Use guide:
That's about 1,320Wh of actual work per day. Apply the same padding as Step 2 (×1.15 for inverter loss, ×1.25 to avoid draining flat) and you're shopping for roughly 1,900Wh of rated capacity to cover a full day comfortably — squarely in the ~2000Wh tier. For output, nothing here is high-draw except the fridge's startup surge, so a station rated around 1,000–1,800W continuous is plenty.
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To ground the tiers in hardware you can actually buy: the Jackery Explorer 1000 (1,002Wh, 1,000W output, 2,000W surge) sits in the "~1000Wh" row — good for a full fridge or short home backup, but its 1,000W ceiling limits big resistive loads. The EcoFlow DELTA 2 holds a similar 1,024Wh but raises output to 1,800W (2,700W surge), so it starts higher-draw appliances the Jackery can't. Same tier by capacity, different tier by output — which is exactly why you size for both.
CPAP machines are a common reason people buy a smaller station, and they're gentler than most assume. A ResMed AirSense 11, for instance, ships with a 65W power supply and runs on 24V DC, but its real draw is far lower in practice — especially with the heated humidifier and tube switched off. That's why even a ~300–500Wh station can carry a CPAP through one or two nights. If you rely on a medical device, always confirm the exact draw and battery compatibility with your equipment provider before depending on it.
The same watt-hour total can be right or wrong depending on the job. For camping and day trips, weight and portability matter, so many people deliberately size down to a 300–600Wh unit and recharge with a foldable solar panel. For van life or extended off-grid, you want enough capacity to ride out cloudy days, so a 1,000–2,000Wh station paired with solar is the sweet spot. For home backup, focus on your critical loads — fridge, a few lights, phones, maybe a CPAP — and a Wi-Fi router, then size to carry them through a realistic outage length rather than trying to power the whole house.
If you're unsure how much you'll need, expandable power stations hedge the bet. Several mid- and large-size stations accept add-on batteries that plug in later — the EcoFlow DELTA 2, for instance, takes a smart extra battery that roughly doubles its 1,024Wh base toward 2,048Wh and beyond. Buying an expandable unit lets you start with what you need now and add capacity if your loads grow, which is often smarter than overspending on a huge fixed battery up front.
Is it better to buy too big or too small? Slightly big. Headroom covers aging cells and future loads; an undersized unit that dies mid-outage helps no one.
Does adding solar change the size I need? Yes — if you can recharge by day, you can often size the battery for one night rather than the entire trip.
What's the one number people forget? Continuous output watts. Capacity gets the attention, but output is what decides whether your appliances turn on at all.
Rather than run these numbers by hand, our power station sizing calculator lets you pick your appliances, set run times, and instantly see the exact watt-hours and output watts to look for — including a surge warning for high-draw devices.