Rechargeable batteries are batteries that can be recharged and used again, unlike the one-time-use batteries. You can buy a battery charger in order to recharge the batteries, and they come in all different sizes, brand names and types. There are alkaline rechargeable batteries, NiMh, and NiCd. When you think these batteries are dead, think again. Sometimes all they need is a little reviving via shock therapy.
Apply the digital multimeter to see what the voltage of the battery is. The normal voltage is 1.2 volts, so if the voltage is less than 1.0 volt, then continue.
Place the red charge of the AC adaptor to the positive end of the battery.
Place the black charge of the AC adaptor to the negative end of the battery.
Count to three.
Remove the AC adaptor from the battery.
Take another reading with the digital multimeter. If the charge is still less than 1.0, unfortunately, the battery is dead. If your multimeter reads 1.2V, then the battery has been successfully revived and can be charged at this point.
This should be done by someone who knows a little bit about electricity and the risks of electrocution by using these two devices. If you do not, find someone who can do this for you. Do not risk electric shock to yourself. AC adaptors as well as digital multimeters can be purchased online, many hardware stores, and many tool stores. Each digital multimeter and AC adaptor has different instructions, so be sure to read your owners manual for further instructions on how to apply them to the batteries.
Exercise extreme caution to avoid shock.