Nickel cadmium (NiCd) were the first rechargeable batteries to be used in power tools. These batteries have the lowest energy density meaning in order for them to produce the same power as a NiMH or Li-ion battery they have to be bigger and heavier. NiCd batteries self-discharge when they aren’t being used. In other words they will lose their charge while being stored. The NiCd battery can be charged over 1,000 times before performance begins to diminish. However, they need to be fully drained of charge once a month or so before recharging to prevent “memory effect” which lessens the charging capacity over time. Leaving these batteries on a charger and only occasionally using them will also shorten their lifespan. Even though these batteries are big and bulky they are still widely used in power tools. They resist impact well and can take heat and cold better than other type of battery. NiCd batteries are also less expensive than NiMh or Li-ion batteries making cordless power tools that use these batteries much more affordable for the weekend do-it-yourselfer.

Nickel metal Hydride (NiMH) batteries have up to 40% higher energy density than NiCd batteries and are more expensive than NiCd batteries. Because of the higher energy density they can be lighter and smaller but still provide the same amount of power. They also suffer from “memory effect” but they only need to be completely discharged once every three months or so to reduce this effect. These batteries should not be overcharged because they can heat up and cause damage to the battery. They are also sensitive to storing conditions and must be stored and maintained properly in order to extend their cycle life. They are more sensitive to heat and cold than NiCd batteries and should be stored and used between 33 and 103 degrees Fahrenheit. NiMH batteries will suffer more damage than NiCd batteries if stored in a deep state of discharge. They are safer for the environment than NiCd batteries because they contain only mild toxins.

Lithium ion (Li-ion) batteries are the most expensive of the three types of batteries but they have an energy density that is twice as much as NiCd batteries and are much smaller and lighter weight. They aren’t affected by “memory effect” so they don’t require much maintenance. Their self-discharge rate is less than half of NiCd batteries. There are some Li-ion batteries that can be stored for 500 days and not need a charge before using. Li-ion batteries are less sensitive to temperature variations than NiMH batteries. The disadvantage of Li-ion batteries is that they age quickly. Their performance is noticeably reduced after only one year.

Cordless power tools are a matter of choice. In most cases they have the same power as electric power tools but are more convenient because there is no need to worry about a power cord. Most people have a mix of cordless tools and electric tools. Cordless drills are probably the most common among cordless tools. It’s not always convenient to have a cord dragging behind when using a drill because they are used in so many different places. A circular saw, on the other hand, is generally used at one location at the jobsite making it much easier to use an electric saw than it is to use an electric drill. However, there are many jobsites that require the use of cordless power tools simply because there is not an electrical outlet nearby.

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