It can be daunting seeing the huge range of cordless power tool batteries on the market but it’s actually much simpler than it seems. They can all be grouped into one of three main types and each cordless power tool manufacturer produces batteries and chargers to fit their products only, which means you are limited by your tool.
The three types of battery all work on the same principle (see How does a cordless power tool battery work?) but have different ‘chemistries’. They are nickel cadmium (NiCd), nickel metal hydride (NiMH) and lithium ion (Li-ion) batteries.
Nickel cadmium (NiCd) rechargeable batteries are very durable and are ideal if you need to use your batteries for regular, intensive work and every day. They respond well to being repeatedly charged and then used up. Leaving them in chargers and only occasionally using them shortens their service life.
They can be recharged over 1,000 times before their performance level starts deteriorating.
They can be recharged and used at lower temperatures than the other chemistries, with fewer negative effects on the battery.
NiCd batteries self-discharge (gradually lose charge even when they’re not being used) during storage but not as quickly as NiMH batteries.
Of the three types, NiCd batteries have the lowest energy density which means that to produce the same power as a NiMH or Li-ion battery they have to be bigger and heavier.
Disposal of NiCd batteries is also an issue as they contain toxic materials which damage the environment. The best option is to recycle them.
Nickel metal hydride
Nickel metal hydride (NiMH) rechargeable batteries’ biggest advantage over NiCd batteries is that they offer up to 40% higher energy density. This means they can be smaller and lighter but still provide the same amount of power. However, they are not as durable.
They are best used for lighter work as high temperatures and heavy use can decrease the service life of the battery from 300-500 charge/discharge cycles to only 200-300.
Although NiMH batteries need to be completely discharged once in a while, they are not as susceptible to memory effect as NiCd batteries.
NiMH batteries contain only mild toxins so are safer for the environment.
They need a longer charge time than NiCd batteries because they heat up easily, which can damage them. They also have a self-discharge rate that is 50% higher than NiCd batteries.
NiMH batteries are about 20% more expensive than NiCd batteries but are often deemed worth it for their higher energy density.
Lithium ion (Li-ion) rechargeable batteries are the most expensive cordless power tool batteries but they are very small and lightweight with an energy density twice that of NiCd batteries.
Also, they don’t require much maintenance because they aren’t affected by the memory effect.
Although they do self-discharge, the rate is less than half that of NiCd batteries. Some Li-ion batteries can be stored for 500 days without needing to be charged on the following use.
On the other hand, they are quite fragile and require a protection circuit that monitors voltage and temperature to prevent damage to the battery. They also age quickly, their performance being noticeably reduced after only a year.
