NiMH chemical composition: Nickel metal hydride (NiMH) batteries are the gold standard in AA and AAA rechargeables to date, so we focused primarily on this variety.As required by our testing criteria, all four of our Li-ion picks are low self-discharge batteries, and they’re rated to last at least 1,000 charge/discharge cycles.

Although they have nominally different capacity ratings and charge differently-the black EBL batteries charge via a Micro-USB port on the sides of their barrels, and the red ones can be charged normally in any charger that’s compatible with Li-ion batteries-they fared about the same in our testing. Similar to their NiMH brethren, multiple Li-ion AA and AAA batteries tied for first in our testing: EBL’s black- and red-labeled AA batteries, as well as its black and red AAAs.

If you own such a device (and if you’re unsure, it’s most likely listed on the bottom of the device or in the manual), you can use a rechargeable Li-ion battery instead of a disposable lithium or alkaline, since all three operate at a constant 1.5 volts. Some electric toothbrushes, digital cameras, and more require a slightly higher voltage than the 1.2 volts that NiMH batteries can provide.

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