Even the latest rechargeable battery will eventually wear out after repeated use. In a new nickel cadmium battery (NiCad), the active materials consist of finely divided crystals. Over time, the crystal size grows and the charge acceptance (capacity) drops. Applying a periodic full discharge reverses this condition, also known as "memory".  Eventually it will wear out and need to be replaced.

            However there are ways to extend the life of rechargeable batteries. If your cordless tool only comes with one rechargeable battery, but an extra one or better yet buy 2. This will allow you to rotate the batteries through heavy use and allow one battery to “rest” and cool down and recharge another one at the same time. It is best to let a rechargeable battery cool down before it is placed back in the charger. Three batteries lets use one, cool one down and recharge the third. You can also save some money by purchasing aftermarket rechargeable batteries too.