A cordless electric drill is only as good as its battery pack. Thus, it is wise to know how to properly charge the pack so that you get the best performance with each charge, longest run time between charges and longest life of the pack. There are a few best practices for charging that will give you all of these benefits.
Put a new cordless drill battery on its charger for a minimum of 18 hours before using it for the first time.
Use the full capacity of the battery between charging for best results. Nearly all drill battery packs are comprised of either NiCd (Nickel Cadmium) or NiMH (Nickel Metal Hydride) cells, and both respond well to this method, which is the opposite of an automobile-type sealed lead battery. Simply put, as a rule of thumb, you should discharge completely and charge completely.
Do not leave a NiCd battery pack on its charger for more than 30 hours. They also will develop a memory that shortens the life between charges if you use it briefly and put it on the charger for short, "quick" charges. The full discharge and charge method is especially important for NiCd batteries.
Discharge a battery pack fully before storing it. Store in cool, dry place of moderate temperature so that it will respond well when it comes time to recharge it.