For cordless tools, follow this advice about the best batteries and chargers.
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Batteries for cordless tools come in varying voltages and amperage hours. With more volts comes more torque or run time depending on the application.
Cordless drills usually come with two batteries so the user can charge one while using the other.
When charging a battery, the cells are being heated. With some batteries, the cells will get too hot and require time to cool down before being charged further. Some chargers have holes to cool the cells more quickly. It may also have a fan built in to speed up the process.
Rechargeable batteries don't really have a 'memory' like they have in the past, but it's still a good idea to let a new battery run all the way down before charging.
Always read the manufacturer's instructions to make sure the tool is being used properly.
Another charger available charges batteries from 7.2 volts to 24 volts. If using batteries from the same manufacturer, batteries can sometimes be charged with a range of voltages using just one charger. Some batteries have to be removed from the charger when they're fully charged.
When the battery reaches its maximum charge, some chargers will provide it with trickle charge, so the battery can be left on the charge when it's complete without hurting the battery.
Nickel-Cadmium batteries can only be charged a certain amount of times. After that point, they will no longer hold a charge. Don't throw them away; recycle.