How to Make Sure Your Portable Generator Is Always Ready

These simple steps will ensure that you’re not left in the dark

Ideally, you don’t use your portable generator often. But you don’t want this key piece of emergency equipment to let you down when you need it. How can you make sure your generator is always ready to run? For answers, Consumer Reports experts weighed in, and we reached out to generator owners who were caught flat-footed in an emergency and had to learn the hard way.

Based on what generator owners told us, keeping fuel in a generator after use is common. And it’s a mistake. “It’s preferable to store the generator without fuel,” says John Galeotafiore, associate director of home improvement testing at Consumer Reports.

Gas-powered generators can sit for months or years without being used, and the fuel in their tanks can go bad, Galeotafiore says. Old fuel can clog up the fuel line and parts of the engine.

To ensure that your gas generator is ready for the next emergency, empty the gas tank by running it until it stops from lack of fuel. Then fill a canister or two of gasoline to keep near the generator for the next time you’ll need it. Store both away from living areas and away from any appliance that could create a spark or flame. (More on that below.) Consumer Reports recommends using a canister that is approved by ASTM International (formerly known as the American Society for Testing and Materials). You can find 5-gallon canisters online starting at just under $50.

To keep the canistered gasoline fresh, add fuel stabilizer. “Each time you run the generator, use gas from that canister in the generator,” Galeotafiore says. “Pour any [leftover] gas from the canister into your car. Then put fresh gas and stabilizer into the canister.”

Why not just put stabilizer directly into the gas in the generator? “After keeping the stabilized gas in the generator for six to 12 months, you need to use it up and start with freshly stabilized gas,” Galeotafiore says. “If it’s in the generator, it’s a lot harder to transfer to your car than if it’s in a gas can.”

To identify problems with your generator and ideally correct them in time, run it periodically—twice a year at least—and again when you learn of an approaching storm, Galeotafiore says. Plug in a hair dryer, a space heater, or another electrical device to make sure the generator is delivering power.

It’s also important to test-run a new generator even if you don’t need it right away, to make sure it runs and to get familiar with its operation. “You don’t want to leave it in the box and only find out there’s an issue when you need it the most,” Galeotafiore says.

You don’t need to turn on the machine for long. For a gas-powered model, just use just a pint or so of gasoline and run the generator until it drains and shuts off, says David Trezza, who leads CR’s generator testing. If your generator runs on propane, there’s no need to run it until it shuts off because propane leaves no problematic residue.

With gas, portable propane, and dual-fuel generators, always run the unit at least 20 feet from your home, with the exhaust pointing away from any structure. Never run it indoors or in a garage, basement, or shed—even if the door is open. Don’t even run it on an attached porch. The generator’s carbon monoxide (CO) exhaust can incapacitate and kill within 5 minutes. In fact, CO from gas-powered generators killed 765 people between 2009 and 2019, a recent Consumer Product Safety Commission report says.

Newer portable generators generally include a CO sensor that shuts off the machine when CO levels go beyond a certain limit. Models without a CO safety shutoff are not eligible to be recommended by CR in our portable generator and inverter generator ratings.

Homeowners that CR contacted about gas generator woes reported a variety of problems when they tried to start their generators after an outage, including old fuel; fouled spark plugs; and gummed-up filters, carburetors, and fuel lines. In some cases, owners could fix or replace parts in time. But not always.

Tim Connon found that his gas generator was suffering from a clogged air intake, which a repair shop speedily fixed. But that problem wasn’t identified until after a week without power in his Palmer, Tenn., home. In the meantime, his family lost food in their fridge and suffered without air conditioning.

“Now I check my generator at least once a year for any issues,” he says. “I realized generators need care and maintenance like a lawn mower.”

In addition to replacing or cleaning all parts, check the engine oil level and add just enough to bring it to the “full” mark on the dipstick. If you can’t diagnose the generator’s ailment after your test run, contact the company if it’s still under warranty, or reach out to a repair shop. If you need to buy a new portable generator, check out CR’s generator ratings.

Even if your generator is ready to run, you’ll need enough fuel to keep it going in the event of a prolonged outage. Keep at least 10 gallons of fresh gasoline for emergencies or two 20-pound tanks of propane.

How long your generator will run on a 10-gallon canister of gasoline depends largely on the machine’s capacity. Here’s what Consumer Reports’ data show for the average run times of the portable generator models in our tests.

Keep in mind that these figures are the averages of all our tested models, so your actual run time will vary. For instance, while we show that 10 gallons of gas can power a midsized generator (5000 to 7000 watts) for an average of 13 hours at a medium to high load, the range is actually about 11 to 22 hours.

Gas-powered generators typically start with a pull cord, but some feature a battery-powered electric start. If that’s the case, make sure to fully recharge that battery every three months or so, Trezza says. Plug the unit into a wall outlet and leave it there for 24 hours. Do the same with portable power stations, which are powered entirely by battery.

Andre Kazimierski of Naperville, Ill., learned the importance of keeping a generator battery charged during a family visit to Colorado when a blizzard knocked out power for 40 hours. “When I tried to start the portable generator, the battery was apparently dead—definitely something I know to check before the storm in the future!” he told CR.

Finding a safe place to store your gas generator and its fuel is a must. Even generators that are emptied of gasoline shouldn’t be stored near appliances or equipment that have the potential to produce a flame or spark. That can include an area housing a water heater or furnace that uses a pilot light or igniter. “Gas fumes can escape and the flame or spark can cause a fire,” Galeotafiore says.

Store your generator—emptied of gasoline—in a clean, dry, and well-ventilated location. Ideally, use a structure that’s not attached to the house, to prevent odors and toxic fumes from entering your home, generator maker DuroMax recommends. If you’re using a shed for storage, consider buying an insulated cover to protect the generator’s machinery from extreme heat or cold, or buy a dedicated enclosure for the generator. Make sure your generator isn’t stored near exhaust sources like vehicle tailpipes or gas-powered outdoor equipment that could inadvertently trigger the generator’s CO alarm, potentially rendering it inoperable. Don’t start your garaged car remotely, which can build up CO.

The importance of good storage ventilation is underscored by an experience Consumer Reports testers had earlier this year, when they couldn’t start up several brand-new units of the gas-powered, portable Ryobi RYi2022VNM inverter generator. When Hong Kong-based Techtronic Industries (TTI), Ryobi’s parent company, examined the units, they learned that the batteries of the generators’ CO sensors—a key safety feature—had been drained while in transit or storage. Though the generators had never been activated, the sensors had apparently worked independently to identify excessive CO, setting off an alarm beep in one generator and disabling all of them. After many hours in that state, the batteries were depleted, though there was no way for users to know that. And because the battery is integrated into the CO sensor module and couldn’t be reached for replacement or servicing, the generators were essentially shut down for good.

TTI says all Ryobi generators have battery-powered CO sensors. “They provide protection from CO even before the generator is powered on, instead of relying on a generator-powered CO sensor which cannot protect a user until the generator is powered on,” a TTI spokesperson said in a statement. “In the event ambient CO conditions are already high (for example near a garage or due to other generators running in close proximity), Ryobi generators will not start or operate thereby preventing an existing danger from becoming worse.”

Ryobi generators have engines designed to shut off at lower CO levels than some other brands’ generators do, a feature Consumer Reports says is worth considering when making a generator purchase. And TTI said the RYi2022VNM’s sensors had properly done their job. Nonetheless, the company removed the few units of this model still on store shelves and offered help for customers who currently own these models and are unsatisfied with them.

Three portable-generator manufacturers we contacted—including market leader Generac, Champion, and Harbor Freight, maker of the Predator brand—said they don’t use batteries to power their CO sensors. “We feel that the battery introduces a potential unnecessary risk into the critical CO safety system, given that generators can typically be stored for several months to years prior to usage in an emergency outage,” a Generac spokesperson told CR.

Consumers can have a leg up on generator safety by purchasing only portable generators in CR’s ratings that pass our CO Safety Technology test. Any model without a CO safety shutoff won’t be eligible to be recommended by CR.

To make the best use of your portable generator—and to better ensure its safe use—have an electrician install a transfer switch. That’s a sort of mini-circuit breaker that sits alongside your main circuit breaker panel. It allows you to power entire circuits in your house with your portable generator, without the hassle and potential dangers of having to run multiple outdoor-rated extension cords from the generator to individual appliances and electronics in your house. You use just one extension cord from the generator to the transfer switch. Then you can power electrical devices using the outlets in your home as you normally do, including appliances like an air conditioner compressor or furnace that’s hardwired to your circuit panel.

Recently CR consumer advocates testified about the need for strong generator safety regulations overseen by the CPSC, which is considering such a standard for the first time. Among other recommendations, CR is urging changes in generator design—such as requiring that a CO sensor battery be accessible and replaceable by a consumer using ordinary tools. Our testers found that they couldn’t do that with the RYi2022VNM’s sealed CO sensor.

Tobie Stanger

Tobie Stanger is a senior editor at Consumer Reports, where she has been helping readers shop wisely, save money, and avoid scams for more than 30 years. Most recently, her home- and shopping-related beats have included appliance and grocery stores, generators, homeowners and flood insurance, humidifiers, lawn mowers, and luggage—she also covers home improvement products like flooring, roofing, and siding. During off-hours, she works on her own fixer-upper and gets her hands dirty in the garden. Follow her on Twitter @TobieStanger.