Rechargeable batteries will typically last for hundreds of charge-discharge cycles, providing an economical and environmentally friendly alternative to disposable batteries in many applications. But rechargeable batteries lose effectiveness over time. Charging creates deposits inside the electrolyte that increase the battery's internal resistance and decrease its charging capacity. Also, if the total stored voltage in a rechargeable battery drops below a certain threshold -- perhaps from being left uncharged for a long period of time -- the battery will no longer accept a charge. However, certain types of rechargeable batteries can be revived and restored. One common type, nickel-metal hydride (NiMH), can sometimes be brought back to life by reconditioning.
Inspect the NiMH battery for physical damage or defects. Do not attempt to use or recondition a battery that is corroded, cracked or otherwise damaged.
If the battery is not completely depleted, deplete its remaining charge completely. Insert the battery into an electronic device and run it until the device no longer operates. Remove the battery and allow it to cool; cool NiMH batteries can discharge more fully than warm NiHM batteries.
Again run the battery in an electronic device until it no longer operates the device. Allow the battery to cool again.
Continue to fully deplete and cool the NiMH battery until it will no longer power a device.
Fully recharge the NiMH battery in an appropriate charger. If the battery does not respond to charging, it is probably beyond recovery.
Repeat steps 3 through 6 -- fully discharging and fully charging the NiMH battery -- three to four times. Any recoverable capacity should be restored.
Some NiMH chargers have "conditioning" or "refresh" features that attempt to recondition the battery automatically using this method. If, after reconditioning the NiMH battery, it still does not provide an adequate charge, it is probably beyond recovery.
Damaged batteries can explode or leak chemicals. Do not attempt to recondition a damaged battery.