Since generators emit carbon monoxide, they require that you take critical safety measures, including running the device outside, at least 20 feet away from any structure.

But in an age when we can charge our smartphones with a battery pack that fits inside a pants pocket, shouldn't there be a simpler way to restore power in the wake of a storm? Or, say, power a campsite without the constant hum of a gas-fueled generator?

Such is the promise of portable power stations, also known as battery-powered inverter generators. Essentially, they're oversized rechargeable batteries—about the size of a countertop microwave oven—that you plug into a typical 110-volt outlet to top off.

When duty calls, you can safely run a portable power station inside, since it doesn't generate any emissions. They have enough capacity to power a few small appliances for a short time. With a host of different outlets (standard 120v outlets, USB ports, and DC chargers), you can use the station to charge electronics, too. And the units often come with portable solar panels, to add more charging capabilities and extend runtime.

“These generators have no fumes and all of the models we tested made virtually no noise,” says test engineer Dave Trezza, who oversees generator testing at Consumer Reports. “But, if these power stations go dead and you’re unable to use your solar panels, you can’t recharge them. You can’t just use another gallon of gas.”

We see models from brands, including Goal Zero, Humless, K2, and Kohler in our portable power station ratings. Some companies, like Goal Zero, market these portable power stations as perfect for apartment preparedness during storms (as opposed to single-family homes with a yard that can accommodate a generator).

In our labs, CR test engineers evaluate five key measures to rate portable power stations: runtime, power delivery, power quality, ease of use, and noise.

To test runtime, we run a constant 300-watt load to simulate powering a TV and a few lights. We also hook each battery up to a side-by-side refrigerator to see how long it lasts. The best model in our tests powered the fridge for 44 hours on one charge (the worst only managed for 13 hours). For power delivery, or how well a model can maintain voltage when tasked with different loads, we use a variety of devices, including a 1⁄2-horsepower submersible pump and a 10,000-BTU air conditioners.

We also judge noise output and found that, as a category, these batteries run quietly: All the models we tested earned an Excellent score for noise.