Rechargeable batteries: chargers, compatibility and recycling

Types and sizes

• AA and AAA rechargeables: usually nickel-metal hydride (NiMH). They replace standard disposable AA and AAA batteries in many devices.
• Lithium-ion: used in phone batteries, laptops and many cordless tools. These are usually sold as battery packs made for a specific device.
• Some devices are sensitive: devices that expect a certain voltage may behave differently with rechargeable batteries, so check the device's manual.
• Low-self-discharge cells: some NiMH batteries are made to hold their charge longer when not in use. The label says so.
• Capacity: shown in milliamp-hours (mAh). A higher number usually means more run time, but check that it suits your device.

Chargers and compatibility

• Use a charger made for the battery type. A NiMH charger is not for lithium-ion, and the reverse.
• Do not mix old and new cells, or different brands and capacities, in the same device or charger slot.
• Check that the charger fits the number and size of cells you have. Some chargers charge cells in pairs.
• Follow the maker's instructions for charging time, and do not leave batteries charging in a hot place.
• Do not recharge disposable (non-rechargeable) batteries.

Our angle: break-even, and the cost people forget

A starter kit with a charger costs more than a pack of disposables, then each charge costs very little. To compare, divide the price of a pack of disposable batteries by the count for the price per battery. Divide the price of the rechargeable kit by that number to see how many disposable batteries it replaces. If you use fewer than that, the kit does not pay for itself. Add the electricity, which is small, and consider how many times you will actually recharge each cell before it wears out. Devices that go through batteries fast, such as game controllers and toys, benefit most. Devices that use batteries rarely, such as smoke alarms and some clocks, may be better with the type the manual says.

1. Divide the disposable pack price by its battery count.
2. Divide the rechargeable kit price by that price per battery.
3. Compare that number with the batteries you really use in a year.

Recycling and disposal

• Do not throw batteries in the household trash or in curbside recycling. Damaged lithium-ion batteries can start fires.
• Many stores and community programs accept used rechargeable batteries for recycling. Check what is available near you.
• Cover the terminals of lithium batteries with tape before you drop them off.
• Store spare batteries in a cool, dry place, away from metal objects.