How we pick power stations
Where every number on this site comes from, and how we turn spec sheets into a pick.
By Jamilur Rahman · Updated
We do not test units ourselves. Picks come from the official spec sheets and manuals, the watt-hour math on this site, and prices we check by hand. This page shows each step, so you can check our work or redo it for your own devices.
What we do and what we don’t
- We don’t test units hands-on. There is no lab and no test bench. We would rather say that plainly than imply otherwise.
- We don’t take free units. No review samples, no loaners, no payment for coverage, no sponsored rankings.
- We do read the official specs. Capacity, output, surge, charge time, weight and battery type come from the maker’s own spec sheet or manual, quoted as given.
- We do the same math everywhere. One formula runs the runtime calculator, every runtime table and every “runs it for about N hours” line in our guides.
The runtime formula
Runtime (hours) = battery watt-hours × 0.85 ÷ average watts.
The 0.85 is the share of the battery that actually reaches your devices. A power station stores DC power and its inverter turns it into AC for your outlets. That step loses heat, usually 10 to 15 percent, and the station’s own fans and screen use a little more. So we count 85% of the rated capacity as usable. On a 1,000 Wh unit, that is 850 Wh.
It is a middle-of-the-road number. Some units do a bit better, and cold weather or an old battery does worse. Treat every runtime here as an estimate, not a promise.
Duty cycles and average watts
Many devices do not draw power all the time. A fridge compressor runs, stops, then runs again. So we multiply the running watts by the share of each hour the device is actually on. We call that share the duty cycle. The result is the average watts, and that is what the formula divides by.
Here is the full-size refrigerator from our data:
- Running: about 150 W while the compressor is on
- On about 30% of the time
- Average: 150 W × 0.3 = 45 W
- On a 1,000 Wh station: 850 Wh ÷ 45 W = about 19 hrs
If you ignored the duty cycle and divided by the full 150 W, you would get about 5.5 hrs. That is the worst case, and the calculator shows it too. Devices like a CPAP, a router or a TV draw steadily, so their duty cycle is 100%.
Start-up surge
Motors and compressors need a short burst of power to start. A fridge that runs at 150 W can need around 1,000 W for a moment as the compressor kicks on. Pumps, air conditioners and power tools are the same, often worse.
The calculator checks two limits before it says yes:
- Continuous output. Everything running at once has to fit under the station’s continuous AC rating. Above 85% of it, we call the fit tight.
- Surge. We take the device with the biggest start-up spike and add everything else that is already running. That total has to fit under the station’s surge rating. If it does not, the answer is no, even if the battery is big.
Runtime tables follow the same rule. If a station cannot start a device, the table says so instead of showing hours.
Where the numbers come from
- Power stations (20 units). The maker’s official product page, spec sheet or manual. If a brand updates a spec, we update ours.
- Device watts (45 devices). ENERGY STAR listings, manufacturer manuals and spec pages, utility company appliance charts and retailer spec sheets, plus a few independent wattage round-ups that we use only as a cross-check and list last. Where sources disagree, we use a typical figure and note the low and high end.
Every device and station page lists the sources behind its numbers.
The table below is the full device list the calculator uses.
| Device | Running | Start-up | On | Average |
|---|---|---|---|---|
| Full-size refrigerator | 150 W | 1,000 W | 30% | 45 W |
| Mini fridge | 100 W | 500 W | 30% | 30 W |
| Chest freezer (7 cu ft) | 80 W | 700 W | 33% | 26 W |
| CPAP (no humidifier) | 7 W | 10 W | 100% | 7 W |
| CPAP with heated humidifier | 34 W | 104 W | 100% | 34 W |
| Portable oxygen concentrator | 40 W | 120 W | 100% | 40 W |
| Home oxygen concentrator (5 L) | 350 W | 1,050 W | 100% | 350 W |
| Nebulizer | 200 W | 300 W | 100% | 200 W |
| Baby monitor | 6 W | 6 W | 100% | 6 W |
| LED light bulb (9 W) | 9 W | 9 W | 100% | 9 W |
| LED string lights | 10 W | 10 W | 100% | 10 W |
| Microwave (1000 W) | 1,500 W | 1,500 W | 100% | 1,500 W |
| Drip coffee maker | 1,000 W | 1,000 W | 100% | 1,000 W |
| Electric kettle | 1,500 W | 1,500 W | 100% | 1,500 W |
| Instant Pot / multicooker | 1,000 W | 1,000 W | 50% | 500 W |
| Induction cooktop (single burner) | 1,800 W | 1,800 W | 60% | 1,080 W |
| Air fryer | 1,550 W | 1,550 W | 60% | 930 W |
| Toaster (2-slice) | 1,200 W | 1,200 W | 100% | 1,200 W |
| Smartphone charging | 20 W | 20 W | 60% | 12 W |
| Laptop (13-16 in) | 65 W | 65 W | 60% | 39 W |
| Tablet | 20 W | 20 W | 50% | 10 W |
| 55-inch LED TV | 90 W | 90 W | 100% | 90 W |
| 65-inch OLED TV | 135 W | 135 W | 100% | 135 W |
| Wi-Fi router + cable modem | 25 W | 25 W | 100% | 25 W |
| Starlink Standard (Gen 3) | 90 W | 100 W | 100% | 90 W |
| Desktop gaming PC | 450 W | 650 W | 80% | 360 W |
| PS5 / game console | 220 W | 350 W | 100% | 220 W |
| Box fan (20 in) | 85 W | 102 W | 100% | 85 W |
| Space heater (1500W) | 1,500 W | 1,500 W | 50% | 750 W |
| Electric blanket | 150 W | 150 W | 50% | 75 W |
| Window AC 5,000 BTU | 450 W | 1,350 W | 50% | 225 W |
| Window AC 8,000 BTU | 735 W | 2,200 W | 50% | 368 W |
| Portable AC 10,000 BTU | 1,100 W | 2,500 W | 60% | 660 W |
| Dehumidifier (50 pint) | 545 W | 1,400 W | 50% | 273 W |
| Sump pump (1/3 HP) | 800 W | 2,100 W | 10% | 80 W |
| Well pump (1/2 HP) | 1,000 W | 3,000 W | 5% | 50 W |
| Washing machine (front load) | 1,000 W | 2,000 W | 50% | 500 W |
| Hair dryer (1875W) | 1,875 W | 1,875 W | 100% | 1,875 W |
| Circular saw | 1,400 W | 3,700 W | 30% | 420 W |
| Cordless drill battery charger | 50 W | 50 W | 80% | 40 W |
| Electric cooler (12V) | 52 W | 98 W | 25% | 13 W |
| Garage door opener | 875 W | 3,200 W | 1% | 8.8 W |
| E-bike charger | 110 W | 110 W | 80% | 88 W |
| Aquarium (55 gal with heater) | 216 W | 216 W | 40% | 86 W |
| Level 1 EV charging (120V) | 1,400 W | 1,400 W | 100% | 1,400 W |
How we check prices
We never show a live price. Prices move every week on Amazon and the brand stores, so a single number would often be wrong by the time you read it. Instead we show the usual street price range, with the date we last checked it. When we recheck a price, the date changes with it.
Always check the store page before you buy. The price at checkout can be higher or lower than our range.
How picks are ranked
Each buying guide is about one job, like a CPAP, a fridge in an outage or a weekend of camping. We rank in this order:
- It has to run the job. Continuous output and surge must cover the devices that guide is about, including start-up spikes.
- How long it runs them. Hours from the formula above, for the devices in that guide.
- Features the job needs. A fast UPS switch-over for a CPAP or a fridge, expansion batteries for home backup, solar input and 12V outputs for camping, low weight if you will carry it.
- Battery life. The rated charge cycles, and whether the battery is LiFePO4, which lasts longer.
- Price for what you get. The usual price range against the capacity and output.
Every pick also says who should skip it. You can check any pick yourself in the calculator or on the “Will it run my…?” pages.
Money and links
Some links on this site are affiliate links. If you buy through one, we may earn a commission at no extra cost to you. No brand can pay to be ranked, included or left out. The details are on the affiliate disclosure page.
Corrections
If you spot a wrong number, a spec that has changed or a claim that does not match the source, email hello@blackoutwise.com. We check it against the source and fix it within a few days. If the change affects a pick or a verdict, we say so on the page and update its date.
Who runs the site is on the about page.