Home Battery System GuideA portable power station is defined by two numbers: watts, the instantaneous power it can supply, and watt-hours, the energy it stores. Anker describes watts as the flow of power and watt-hours as the size of the fuel tank. Because inverters lose energy converting DC to AC, Anker estimates real runtime at 85 to 90 percent of the rated watt-hours divided by the appliance load.
Watts versus watt-hours
Two specifications decide what a portable power station can do. Anker explains that watts measure how much power the station can supply at one moment, so your combined appliance load must stay below the continuous AC output rating. If a station is rated 1,000 watts continuous, the devices you plug in at once have to add up to less than that.
Watt-hours describe the tank size. Anker states that watt-hours tell you how much energy the battery stores, using the analogy of watts as the flow of power and watt-hours as the size of the fuel tank. A station can have plenty of stored watt-hours yet still be unable to start a high-wattage appliance if that appliance exceeds its instantaneous watt rating.
What common devices draw
Small electronics are easy to run and large motor or heating appliances are not. Anker lists smartphones drawing 5 to 20 watts while charging, CPAP machines without a heated humidifier at 30 to 60 watts, LED TVs at 50 to 150 watts, and mini fridges at 50 to 150 watts while running.
Heavier appliances climb quickly. Anker puts full-size refrigerators at 100 to 800 watts running and microwaves at 900 to 1,500 watts input. Anker groups the easy loads, phones, laptops, Wi-Fi routers, LED lights, fans, CPAP machines, TVs, and mini fridges, as within reach of most stations, while refrigerators, microwaves, coffee makers, power tools, and select AC units need larger models.
Estimating runtime
Runtime is the stored energy divided by the load, adjusted for conversion losses. Anker gives the formula estimated runtime equals battery watt-hours multiplied by 0.85 to 0.90, divided by appliance watts, accounting for 85 to 90 percent inverter efficiency.
Anker's worked example takes a 1,000 watt-hour station powering a 100 watt device and arrives at roughly 8.5 to 9 hours. The same math shows why doubling the load roughly halves the runtime, and why a device that sits near the station's continuous watt rating will drain the tank fast.
The refrigerator surge to plan for
Refrigerators are the appliance buyers most often want to back up, and they behave in a way that raw wattage hides. EnergySage explains that a refrigerator cycles on and off, so its running draw is much lower than its rated wattage, and suggests dividing the rated wattage by three to estimate real running consumption. By that rule a 500 watt refrigerator uses about 167 running watts.
The catch is the startup surge. A refrigerator's compressor briefly pulls two to three times its running wattage when it kicks on, so a portable station must supply that momentary spike, not just the average draw. Sizing to the surge, and confirming the station's continuous and peak watt ratings, keeps the fridge from tripping the unit when the compressor starts.