Battery Overview

Thanks to improved batteries, cordless power tools have become really powerful. At the same time, the prices have come down. Not only have batteries become more powerful but they can hold a charge longer. Thanks to rapid chargers, it is possible to work non-stop, except for time it takes to change batteries, with just two batteries.

Not all batteries are created equal and prices vary a lot. Batteries are often rated according to Ah, amp-hour. But actually Ah is not especially interesting. Ah measures how much energy can be stored in a battery. Ah is simply the current, in ampere, multiplied with the time of discharge, measured in hours. A battery rated at 20 Ah delivers, in theory, 1A for 20 hours before it is completely discharged.

There are three main types of batteries in use today:
– Nickel cadmium (NiCad)
– Nickel metal hydride (NiMH)
– Lithium-ion (Li-Ion)

Nickel cadmium batteries are the oldest, developed already back in 1899. NiCad batteries are still used today. The nominal cell voltage is 1.2V and they can be charge more than 1,000 times. The main advantage of NiCad batteries is that they are relatively cheap. Additionally, they can be charged quickly, although not as quickly as Li-Ion batteries. Ni-Cad batteries are also 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 becomes 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 suffer from memory effect problems and will self-discharge about 10% per month.

Nickel Metal Hydride batteries are newer than NiCad batteries. They have the same nominal cell voltage as NiCad batteries, 1.2V. Compared with NiCad they have higher capacity and are less toxic. NiMH batteries have memory effect problems but less so than NiCad batteries. NiMH batteries can not be recharged as many times as Ni-Cad batteries, generally up to 1,000 times. They also have higher self-discharge than NiCad and lithium-ion batteries. The self-discharge is generally 30% per month or more, compared to 10% for Ni-Cad batteries and between 5-10% for lithium-ion batteries. Lately, NiMH batteries have had trouble competing with lithium-ion batteries.

Commercial lithium-ion batteries were introduced in 1991. Nowadays lithium-ion batteries are used a lot in consumer electronics. 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 cordless tool 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.

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