As temperatures remain frosty across much of the nation, cutting the grass, trimming hedges, and other outdoor chores seem far off. But now is a good time to check the lithium-ion batteries for your cordless electric mower and other battery-powered outdoor tools. 

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The batteries that power your mowerstring trimmer, or leaf blower are expensive to replace, which makes keeping them in working order all the more important. "Even without a gasoline engine to winterize, you'll need to take other steps to protect your lithium-ion batteries from damage during long stretches of storage," says Dave Trezza, who oversees our testing of string trimmers, leaf blowers, and other outdoor power equipment. Use these tips from our pros:

Store Batteries Indoors

Even if you store the tools themselves in a garage or shed, bring the batteries inside. Extreme temperatures can shorten the life span of the cells inside batteries and cause them to fail prematurely. Keeping them indoors minimizes temperature fluctuation. Check the owner's manual for an exact range, but most batteries do best when stored between 40° F and 80° F.

Keep the Charge at 40 Percent

If it’s going to be 30 days or longer before you next use your lithium-ion battery to power a tool, try to charge—or discharge—the battery to roughly 40 percent of its capacity. Some batteries display the charge right on the battery or the charger.

Others rely on a series of four lights—indicating that the battery is at 25, 50, 75, or 100 percent of capacity. If you have one of these, run the battery in a tool until right after the 50 percent light goes off, indicating that the battery is somewhere between 25 and 50 percent of capacity.

Remember to check the owner's manual—some batteries have embedded software that will discharge to the optimal level after going unused for a prolonged period. 

Check Your Manual

Some lithium-ion batteries do well with a charge in the middle of the storage season; others don't require one. Check the manual to see what the manufacturer advises.

Ego, whose lawn mower, string trimmer, leaf blower, and chain saw have all performed well in Consumer Reports’ tests, says its gear doesn’t require any midseason charging.

GreenWorks, however, advises charging the battery to full capacity every two months when it’s in storage, then draining it back down to 40 percent.

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