What size power station do I need?
Multiply the watts of each thing you want to run by the hours you want it running, add them up, and divide by 0.85. The result is the battery capacity in watt-hours (Wh) to shop for. Then check three more numbers: continuous AC output, surge output and recharge speed. This page walks through the worksheet, a worked example and the checklist, so the math comes before the sale price.
How this guide was made: this is a research guide built on manufacturer specifications and federal guidance, with sources linked throughout. We haven't bench-tested any of the equipment mentioned, and we don't claim to. Specs for the EcoFlow DELTA 2 and Bluetti AC200MAX come from their published manuals.
Watts vs watt-hours
- Watts (W) are how fast something uses power right now. A router might draw 20 W.
- Watt-hours (Wh) are the amount of energy used over time. That router at 20 W for 12 hours uses 240 Wh.
- A power station is rated in Wh (its tank) and in W (how fast it can pour). You need both to be big enough.
The 0.85 divisor is a planning assumption for conversion losses between the battery and your device. Our power station runtime calculator uses the same 85%. Real losses vary by model, load and temperature, so treat it as a reasonable default, not a measurement.
Step 1: List your loads
Start from the numbers in the appliance wattage chart, which cites Honda and Champion charts, and replace them with figures from your own appliance labels. Some typical ranges from Champion's chart:
| Load | Running watts |
|---|---|
| Router or modem | 10–20 W |
| LED bulb | 8–15 W each |
| Phone or laptop charger | 20–100 W |
| TV (32"–55") | 80–400 W |
| CPAP, no heated humidifier | 30–60 W |
| CPAP with heated humidifier | 60–120 W |
| Refrigerator | 150–400 W running, 800–1,200 W starting |
For the refrigerator, average watts are much lower than running watts because the compressor cycles. Our refrigerator guide shows how to work out the average from the EnergyGuide label; we use about 67 W as an example there.
Step 2: Worksheet
For each load, write watts, hours and Wh (watts × hours). Then total and divide by 0.85.
| Load | Watts | Hours | Wh |
|---|---|---|---|
| Total at the devices | |||
| Battery needed (total ÷ 0.85) |
Step 3: A worked example
Assumptions: average fridge-freezer 67 W, router 20 W, 100 W of LED lights, a CPAP at 60 W, and 100 W for phone and laptop charging. These are assumptions for the example, not a promise about your home.
| Load | Watts | 12-hour night | Wh | 24-hour day | Wh |
|---|---|---|---|---|---|
| Fridge-freezer (average) | 67 | 12 h | 804 | 24 h | 1,608 |
| Router and modem | 20 | 12 h | 240 | 24 h | 480 |
| CPAP (see CPAP backup power) | 60 | 8 h | 480 | 8 h | 480 |
| LED lights | 100 | 3 h | 300 | 5 h | 500 |
| Phone and laptop charging | 100 | 2 h | 200 | 4 h | 400 |
| Total at the devices | 2,024 | 3,468 | |||
| Battery needed at 85% | about 2,381 | about 4,080 |
Reading it: a night needs a battery near 2.4 kWh, and a full day about 4.1 kWh. Compare that to two real units whose specs the makers publish (see generator vs power station):
| Unit | Capacity | Usable at 85% | Share of the 12-hour night | Hours of the 24-hour day |
|---|---|---|---|---|
| EcoFlow DELTA 2 | 1,024 Wh | about 870 Wh | about 43% | about 6 h |
| Bluetti AC200MAX | 2,048 Wh | about 1,741 Wh | about 86% | about 12 h |
(Hours of day: usable Wh divided by 3,468 Wh, times 24, assuming the load is spread evenly.) So a mid-size unit gets you through a night or part of one, not several days, without recharging.
Step 4: Check output watts and surge
Capacity is only the tank. Output decides whether the unit can power things at the same time and start motors.
- Add up running watts of everything on at once. In the example, using the upper Champion refrigerator figure of 400 W: 400 + 20 + 100 + 120 (CPAP at its upper figure) + 100 = 740 W.
- Add the largest start surge. A refrigerator's start extra is its starting minus running watts: 1,200 − 400 = 800 W. Standard method: 740 + 800 = 1,540 W. Conservative: 740 + 1,200 = 1,940 W. This is the same method as our generator size calculator.
- Compare to the spec sheet. EcoFlow lists the DELTA 2 at 1,800 W continuous and 2,700 W surge; Bluetti lists the AC200MAX at 2,200 W continuous and 4,800 W surge (see the manuals linked in the sources). The 740 W running total fits comfortably and the 1,540–1,940 W start totals fit under the surge ratings. That is arithmetic on published numbers, not a test result, so check your own fridge's label and the manufacturer's guidance.
If you need a 240 V appliance such as a well pump, central AC or an electric dryer, check the spec sheet for 240 V output before anything else. Most portable stations are 120 V only, and large loads drain a small battery in minutes.
The first-time buyer checklist
| Check | What to look for |
|---|---|
| Capacity (Wh) | At least your worksheet total, with margin |
| Continuous AC output (W) | Above your running total; leave headroom |
| Surge (W) | Above the standard-method start total; check how long the surge lasts |
| Waveform | Pure sine wave AC output if you run electronics or medical devices |
| Ports | The right mix of AC outlets, USB-C power delivery, USB-A and 12 V DC for what you own |
| Recharge speed | Max AC input and solar input watts (see below) |
| Temperature range | Charge and discharge limits, which are published for the DELTA 2 (charge 32–113 °F, discharge 14–113 °F) and the AC200MAX (charge 32–104 °F, discharge −4–104 °F) |
| Pass-through / UPS mode | Switchover time. EcoFlow's manual quotes 30 ms for the DELTA 2 and warns against 0 ms-sensitive gear |
| Weight and size | The DELTA 2 is 27 lb and the AC200MAX is 61.9 lb |
| Warranty and support | Length, what it covers, who services it |
| Safety certification and recalls | Certification named in the manual, and a check of CPSC recalls and warnings |
Recharge time and solar
Recharge time is capacity divided by input watts, at best: the DELTA 2's 1,024 Wh at its 1,200 W AC maximum is about 0.9 hours, and the AC200MAX's 2,048 Wh at 500 W (its T500 AC adapter's maximum charging power) is about 4.1 hours. Real times are longer because charging slows near full. Solar input is limited by the panels and the sun. As an assumption for planning: panels averaging 200 W over 5 hours deliver about 1,000 Wh on a good day, far less on a cloudy one.
If your outages last days, a recharge source (solar, a car, or a small generator run outdoors) matters as much as capacity. See generator vs power station.
Before you buy during a sale
- Decide the Wh first. Use the worksheet, then compare models on capacity and output, not on a "peak watts" headline.
- Compare price per Wh at purchase time. Divide price by watt-hours. We don't list prices because they change.
- Skip sellers you can't verify. CPSC has issued warnings and recalls about specific power stations that caught fire, including a warning about Aeiusny power stations and the HALO 1000 recall. Search CPSC's recall list for any model you consider.
- Buy for the use case. An apartment night kit is a different purchase than a hurricane kit. See renters' backup power.
Using it safely
The U.S. Fire Administration says to store lithium-ion batteries at room temperature when possible, not to charge them below 32 °F or above 105 °F, and to stop using any that give off an odor, change shape, leak or overheat (USFA). Use the maker's charger, keep it on a hard surface away from bedding, and try the whole setup in daylight before you need it.
For medical equipment, check your device's rating and ask your provider; this page is not for life-support planning. See CPAP backup power for a sleep-apnea machine.
Summary
Watt-hours = watts × hours ÷ 0.85, then check continuous output, surge, recharge speed and temperature limits. For a modest essentials list, expect roughly 2.4 kWh for a night and 4 kWh for a day. Run your own list through the power station runtime calculator, then read the Alabama outage checklist to finish the plan.