Portable power stations explained: what they do at home

What a portable power station is

Anker SOLIX defines it as "a rechargeable battery system that stores electricity and provides power when a traditional wall outlet is unavailable." ¹ It says the unit "combines a battery, battery management system, inverter, and output ports into one device." ¹

Think of a big power bank with household outlets. You charge it, carry it, and plug things into it.

Here's what each part does:

- Battery: stores the energy. - Battery management system: watches the battery while it charges and discharges. - Inverter: turns the battery's stored power into the AC power that standard plugs use. - Output ports: AC outlets, plus USB and other ports.

It's not wired into your home. That's the main difference from the batteries in our guide to home battery backup.

How a portable power station works

Power goes in one direction. Anker SOLIX describes it this way: "Energy moves through the unit in one direction." ² It then "exits through the inverter or the DC ports depending on what you plug in." ²

You can refill the battery from several sources. Anker SOLIX says the unit "stores electricity from charging sources such as wall outlets, solar panels, or vehicle charging." ¹

EcoFlow gives one example. For its DELTA 2, it lists solar charging with "up to 500W input" and says the unit can "auto-switch to battery power when the grid goes down" in EPS (emergency power supply) mode. ³ Not every model does that, so check the maker's page for the one you're considering.

Watt-hours and watts: the two numbers that matter

Every power station has two headline figures.

Watt-hours (Wh) is the size of the tank. Anker SOLIX says "battery capacity determines how much energy a power station can store and is usually measured in watt-hours." ¹ One kilowatt-hour (kWh) is 1,000 Wh.

Watts (W) is how much the unit can supply at once. Anker SOLIX says "the inverter's output capacity determines which appliances the power station can support." ¹

A real example: EcoFlow says "DELTA 2 lets you store 1kWh" and offers "a huge 1800W output." ³ Those are the maker's figures.

Add up the watts of what you want to run. If the total is above the unit's output, it won't carry the load.

How long it will run: a worked estimate

Anker SOLIX gives the theory: "A 500Wh unit can theoretically supply 500 watts for one hour." ² In practice it runs a bit less, because of conversion losses. ²

Here's an estimate for a 1 kWh (1,000 Wh) unit, the size EcoFlow lists for the DELTA 2. ³ We assume 90 percent of the stored energy is usable, to allow for conversion losses. That 0.9 is our own assumption, not a maker's figure.

- Load: a 100 W device. Runtime: 1,000 Wh × 0.9 ÷ 100 W = about 9 hours. ³ - Load: a 300 W device. Runtime: 1,000 Wh × 0.9 ÷ 300 W = about 3 hours. ³

These are our estimates, not a maker's promise. Real runtime depends on the load. Anker SOLIX says "runtime depends on battery capacity, inverter output, and the actual power draw of connected devices." ²

Check the label on each appliance for its watts. If a device only lists amps and volts, multiply them.

What it can back up at home

Think essentials. Anker SOLIX advises: "For home backup, focus on essential loads rather than trying to power the entire house." ¹

A power station isn't a whole-home system. If you want the whole house kept running, that's a different product, and it needs an electrician.

EcoFlow calls the DELTA 2 "ideal for home power backup, RVs, tents, or on the go." ³ That's the maker's description of its own product, not a test of ours. We haven't used this equipment.

Safety: never plug it into a wall outlet

Don't connect a power station to your home's wiring with a cord and a wall outlet. One electric cooperative, Poudre Valley REA, says backfeed is hazardous "to the neighboring properties, and to our lineworkers and other first responders." ⁴

The same utility says: "A transfer switch helps prevent backfeed by safely isolating the power source from its primary source to a backup or secondary source." ⁴ Fitting one is a job for a licensed electrician.

Plug appliances straight into the power station's own outlets. If you want a battery that feeds the house circuits, a licensed electrician must install it.

For use and placement, follow the maker's manual. Anker SOLIX says to follow the manufacturer's instructions, "keep vents clear," and "avoid extreme temperatures." ²

What to compare before you buy

Put the maker's figures side by side. Don't rely on a single headline number.

- Capacity (Wh or kWh): how long it lasts. - Output (W): what can run together. - Battery chemistry and cycles: our page on LiFePO4 battery life and charging explains the chemistry. EcoFlow lists "LiFePO4 battery chemistry giving you 3000+ full charge and drain cycles" for the DELTA 2. ³ - Warranty: EcoFlow says "warranty extended to 5 years" for that model. Read the terms on the maker's page. ³ - Charging options: wall, solar or car. - Price: it changes often. Check the maker's own page for the current US dollar price and its date.

Our page on home battery backup covers the wired-in alternative.