Rechargeable batteries are either nickel-based or lithium-based. Lithium-based batteries, such as lithium ion (Li-Ion) and lithium polymer (LiPo),weigh less, produce higher voltage, have greater endurance and, importantly, don't suffer from what's referred to as the "memory effect" associated with nickel-based batteries. The memory effect is when you charge your battery until full, but after using it for a short period, it goes dead. However, if you have nickel-based batteries that have gone bad, it's likely you can revive them.
Put your bad rechargeable batteries into your charger. Turn on your charger and let your batteries charge until full. Bad rechargeable batteries will still take a charge, even if charging them only takes a few minutes.
Turn off your charger and remove the batteries from the charger. Insert your batteries into the electrical item they power.
Turn on your electrical item and let it operate until it stops, or automatically turns off. It's not likely to take long, as bad rechargeable batteries are unable to retain energy.
Remove the rechargeable batteries from the electrical device. Leave them out of the device for about 30 minutes, or until they are cool to the touch, whichever is longer.
Replace the batteries into the electrical item and turn it on. You may find it does power up, despite it not working previously. Let the electrical item operate until it stops or turns off. Remove the batteries and let them rest for 15 minutes.
Repeat the process of putting the batteries into the electrical item, powering it up and letting it run until it stops. Do this until your electrical item doesn't power up. Each time you repeat the procedure, the crystals in the rechargeable batteries discharge a little energy. This breaks down the crystals making them smaller; the smaller the crystals, the more energy your batteries can retain.
Put your batteries into the charger. Turn on the charger and let the batteries charge until full. Expect it to take considerably longer than you are used to. Breaking down the crystal by using a deep discharge has revived the batteries and they can now retain more energy.
Turn off the charger and remove the batteries once they are fully charged. Insert them into your electrical item and use it normally.