The battery in your cordless drill is very important. A good battery makes life much easier, you get a powerful drill and can work a lot before the battery needs to be charged. Poor batteries on the other hand don’t last long and may still take a long time to charge.
Today, you have three main types of batteries to choose from. They are:
- Nickel Cadmium (NiCd or NiCad)
- Nickel Metal Hydride (NiMH)
- Lithium Ion (Li-Ion)
Nickel Cadmium batteries were the first batteries to be used in cordless drills and they are still used today. They are relatively cheap and can be charged many times, up to 1,000 times. Additionally, they can be charged quickly, although not as quickly as Li-Ion batteries, and Ni-Cad batteries are less sensitive to temperature than NiMH. The latter means that they can be used in both cold and hot environments. But if the battery itself is hot, charging can become a problem. The main drawback is that they are toxic. Cadmium is a heavy metal that needs to be recycled properly. Ni-Cad batteries also have memory effect problems. Note that Ni-Cad batteries are banned in EU.
Nickel Metal Hydride batteries are newer than Ni-Cad batteries. Compared with Ni-Cad they have higher capacity and are less toxic. NiMH batteries have memory effect problems but less so than Ni-Cad batteries. But NiMH batteries can not be recharged as often as Ni-Cad batteries. They also have higher self-discharge rate than Nickel Cadmium batteries. The self-discharge is generally 30% per month or more, compared to 10% for Ni-Cad batteries and between 5-10% for Li-Ion batteries.
Lithium-ion batteries are the newest of the three main battery types. Lithium is light-weight and possesses very good electrochemical characteristics. But it is an unstable metal, for safety reasons pure lithium is not used in batteries. For most purposes, Li-Ion batteries are the best but also the most expensive. They have the highest capacity, are light-weight, no memory effect and low self-discharge rate. The life time of Li-ion batteries is about three to five years, regardless of how much they are utilized. As expected, most high-end tools are using Li-Ion batteries. If you are going to use your drill a lot, paying extra for the powerful but light-weight Li-Ion batteries is well worth considering. The Li-Ion batteries are also considered to be environmentally safe.
Ni-Cad and MiNH batteries suffer from memory effect. It refers to the fact that batteries have lost their maximum capacity after being repeatedly recharged before the battery was flat. For some unknown reason, the batteries seem to remember the smaller capacity and forgotten the original capacity. Note that Li-Ion batteries have no memory effect. Also note that memory effect has nothing to do with the age of the battery. All rechargeable batteries will lose storing capacity over time, due to secondary chemical reactions within the battery.
Batteries have an Amp Hour (AmH) rating. It indicates how much energy can be stored in the battery, thus measuring the capacity of the battery. It is the current flow, in Ampere, multiplied by the time of discharge, in hours. If a battery is rated at 20 AmpH, it can sustain a 1 Ampere draw for 20 hours. Just bear in mind that the listed AmH for different batteries may not have been measured in the same way, so higher AmH does not guarantee that the battery is better.