The sheer range of power tool batteries on the market may seem intimidating, but it's actually a lot easier than it looks. They can all be grouped into one of three main types, and each cordless power tool manufacturer makes batteries and chargers for their products only, which means you are limited to your tool.
All three types of batteries work on the same principle (see. How does a cordless power tool battery work?), but have different chemistry. These are nickel-cadmium (NiCd), nickel-metal hydride (NiMH) and lithium-ion (Li-ion) batteries.
Battery voltage and capacity are other major differences between batteries. They are discussed in more detail on the page What sizes and weights of batteries for cordless power tools are available?
Nickel Cadmium
Nickel Cadmium (NiCd) batteries are very durable and ideal if you need to use batteries for regular, intensive work and every day. They respond well to repeated charging and then used up. Leaving them in chargers and using them only occasionally will shorten their lifespan.
They can be recharged over 1,000 times before their performance level starts to degrade.
They can be recharged and used at lower temperatures than other chemicals with less negative impact on the battery.
NiCd batteries self-discharge (slowly lose their charge even when not in use) during storage, but not as quickly as NiMH batteries.
Of the three types, NiCd batteries have the lowest energy density, which means they need to be larger and heavier to deliver the same power as a NiMH or Li-Ion battery.
They also need to be discharged and then recharged regularly to prevent the "memory effect" (see below). How to charge a nickel battery for power tools), which stops the battery.
Disposal of nickel-cadmium batteries is also a problem because they contain toxic materials that are harmful to the environment. The best option is to recycle them.
Nickel metal hydride
The biggest advantage of nickel metal hydride (NiMH) rechargeable batteries over NiCd is that they provide up to 40% higher energy density. This means they can be smaller and lighter, yet still provide the same amount of power. However, they are not as durable.
They are best used for lighter jobs, as high temperatures and heavy use can shorten battery life from 300-500 charge/discharge cycles to 200-300.
Although NiMH batteries need to be fully discharged from time to time, they are not as prone to memory effects as NiCad batteries.
NiMH batteries contain only mild toxins, so they are more environmentally friendly.
They require a longer charge time than NiCd because they heat up easily, which can damage them. They also have a self-discharge rate that is 50% faster than NiCd batteries.
NiMH batteries are about 20% more expensive than NiCd batteries, but are often considered worth it due to their higher energy density.
Lithium-ion
Lithium is a light metal that readily forms ions (see How does a cordless power tool battery work?), so it is ideal for making batteries.
Lithium-ion (Li-ion) rechargeable batteries are the most expensive cordless power tool batteries, but they are very small and light and have twice the energy density of nickel-cadmium batteries.
In addition, they do not require special care, since they are not subject to the memory effect.
Although they self-discharge, the rate is half that of nickel-cadmium batteries. Some lithium-ion batteries can be stored for 500 days without needing to be recharged the next time they are used.
On the other hand, they are quite fragile and require protection circuitry that monitors voltage and temperature to prevent damage to the battery. They also age quickly, their performance is noticeably reduced after a year.
