GUIDE
How to Size a Portable Power Station
A power station is a battery with outlets. Two numbers decide whether one fits: how much energy it holds, and how much power it can deliver at once. Most buying mistakes come from mixing those up.
Watts and watt-hours
Watts (W) measure how hard a device pulls right now. Watt-hours (Wh) measure how much energy a battery holds. A 245 Wh battery can supply 245 watts for one hour, or 24.5 watts for ten hours, before losses.
Step 1: Check the output limit first
Every power station has a rated output, and many list a higher surge or boost figure for short bursts. Add up the running watts of everything you plan to run at the same time. That total has to stay under the rated output, and the biggest starting surge has to fit under the surge figure.
If a device is over the limit, no amount of battery capacity will fix it.
Step 2: Work out the energy
Use this:
Energy needed (Wh) = running watts x hours of use x duty, divided by 0.85
- Duty is the share of time a device is actually drawing power. A refrigerator cycles on and off, so a duty of about 40 percent is a fair estimate. A router runs all the time, so use 100 percent.
- 0.85 is a rough allowance for conversion losses. Real results vary by model and load.
Example
| Device | Watts | Hours | Duty | Energy (Wh) |
|---|---|---|---|---|
| Wi-Fi router and modem | 30 | 12 | 100% | 360 |
| LED lights | 20 | 5 | 100% | 100 |
| Laptop | 60 | 4 | 100% | 240 |
| Phones, two full charges | about 30 | |||
| Total | 730 |
Divide by 0.85 and you get about 860 Wh. A buyer would look for a unit of 900 Wh or more, not 245.
What a small unit can do
The EcoFlow RIVER 3 is listed at 245 Wh, with a 300 W rated output and up to 600 W with its X-Boost feature. That is a good fit for a router, a few lights, phones and a laptop. Using the same math, a 60 W laptop would run for about three and a half hours on it. A 10 W lamp would run for about 20.
It is not a fit for a space heater, a kettle or a well pump, which draw more than 300 W. A full-size refrigerator may exceed the surge rating at start-up, so check the fridge's starting watts first.
Recharging
Check how the unit recharges and how fast. Most take wall power, a car outlet or a solar panel. A battery you cannot recharge during a long outage is a short-term fix. If the outage may last days, plan for solar or a generator to top it up, run outside only.
Battery type and life
Many newer units use lithium iron phosphate (LiFePO4) cells, which makers rate for thousands of charge cycles. Check the cycle rating and the warranty.
Safety
- Power stations make no exhaust and can sit indoors. Keep one off soft surfaces and away from heat and water.
- Follow the maker's instructions on ventilation, temperature and storage.
- For life-support or medical equipment, do not assume a power station is suitable. Ask the device maker, and see our guide on medical devices in an outage.
What to do next
- Run your list through the wattage calculator.
- Compare with our guide on generator or power station.
Sources
- EcoFlow RIVER 3 listing with specifications (Adorama): https://www.adorama.com/ecoefriver3u.html
- RIVER 3 specifications and testing notes: https://www.dreambigtravelfarblog.com/blog/ecoflow-river-3-review-245wh-power-station
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