With so many power tools going cordless these days, and so many options for batteries and voltage in those tools, it raises a lot of confusion for the buyer. Does the battery type really affect the tool’s usability? How about voltage: do higher voltage tools really deliver more power? Or, is all of this hoopla just a bunch of advertising hype, intended to impress the uninformed and get them to buy?
These are good questions, but unfortunately they are hard questions to find answers for. In this article, I’m going to try and give you a short-course on rechargeable batteries, help you get through the advertising hype and make informed decisions.
To start, there are three basic specifications that affect the performance of a rechargeable battery, and in turn affect the performance of any tool containing those batteries. These are:
- Battery material type
- Battery voltage
- Battery capacity (measured in amp-hours)
Like always, there is a trade-off in each of the battery types we’re going to look at, in addition to the trade-offs in cost, life expectancy, environmental tolerance, and recharge time.
There are three basic materials used in cordless tool batteries; NiCd (Nickel Cadmium, sometimes written Ni-Cad), NiMH (Nickel-Metal Hydride), and Li-ion (Lithium Ion):
- NiCd batteries are the oldest of these three types of batteries, having been in use for industrial purposes since the 1950’s. Because of this long history, NiCd batteries are the most economical true rechargeable batteries on the market. NiCd batteries are commonly available in AA size, which makes them convenient for replacing standard AA batteries in all types of electronic products. Another great advantage of these batteries is their long life; a NiCd battery can last up to 1500 charge cycles. Unfortunately, a AA NiCd is only 1.25 volts, instead of the 1.5 volts found in non-rechargeable AA batteries. Another disadvantage of NiCd batteries is that they have a very low energy density, meaning that they have to be recharged sooner than other types of rechargeable batteries.
- NiMH batteries were the first effort at replacing NiCd batteries as the standard rechargeable battery. Their main plus over NiCd is their energy density is about 50 percent higher than NiCd batteries. This means that one can drill 50% more holes or cut 50% more material before needing a recharge. Unfortunately, NiMH batteries don’t handle recharging well, and only last 1/3 to 1/5 of the number of charge cycles of NiCd batteries. It is this problem which has kept NiMH batteries from taking over from NiCd, except in some limited electronics applications.
- Li-ion batteries are the new kid on the block – at least as far as cordless power tools are concerned. The truly great thing about these batteries is that they have double the energy density of NiCd batteries, allowing the user to complete double the work between recharges. With the newer Li-ion cordless power tools, special circuitry is built into the battery charger, allowing these batteries to recharge (to an 80% charge level) in as little as 30 minutes. That means that on the average job, a worker (such as a construction worker) may not even need a second battery. They are also much lighter, reducing operator fatigue. Although not as long-life as NiCd batteries, these batteries will last up to 1,000 charge cycles. The downside to these excellent batteries is the cost. Since it is a new technology on the market, batteries cost about double the cost of comparable NiCd batteries.
The current trend is towards producing more cordless power tools that use Ni-ion batteries. It is expected that this trend will allow the price of these batteries to drop, overcoming the only negative point against them.
Obviously, battery voltage has to be matched to the tool that the battery is being used in. Putting a battery with a higher voltage rating into a tool will damage the tool, while putting a battery with too low a voltage rating in a tool will not provide enough power for the tool to work efficiently.
There has been a trend through the last thirty or more years to increase the voltage of cordless tools and their corresponding batteries. This trend has increased in the last ten years. One of the common advertising points mentioned about a cordless tool is its voltage. Does this make a difference? Yes, it does.
To put it simply, the higher the motor voltage (which is what they are really talking about), the more power, or the more torque the motor can produce. This relates directly to the amount of drive power in the tool. In other words, a higher voltage cordless drill can drive screws into harder wood, and a higher voltage cordless saw can make deeper cuts through harder woods.
The same tool may be made by the same manufacturer in a 12 volt and an 18 volt version. While the higher voltage version will probably cost more, it’s a worthwhile investment. The extra power will allow you to use that tool for things you can’t use the lower voltage tool for.
The easy way to prove this to yourself is to compare any cordless power tool you have to a corded tool of the same type. Take a cordless drill for example. Try driving a two inch drywall screw into a dry 2 x 4 stud. There’s a good chance you’ll never get that screw to go all the way in (unless you use soap or oil to lubricate the screw). Then try the same thing with a corded drill. You will probably not only be able to drive the screw in, but it will go faster, and possibly end up with the screw head below the surface of the wood.
Battery capacity refers to how much of a particular voltage a battery can hold. You can think of it this way; if you get gas for the lawnmower, which is better, use a 1 gallon gas can, or use a 5 gallon gas can? Obviously, the 5 gallon gas can holds more fuel, preventing you from having to make another trip to the gas station as soon.
Batteries have this same difference in capacity. When comparing two power tools, this is an important thing to take into account. A battery with a higher capacity will be able to drill more holes, sink more screws, or cut more wood than one with a lower capacity.
Some manufacturers make more than one version of their batteries. They may have a low capacity 18 volt Li-ion battery and a high capacity version of the same battery. If you are only using your cordless power tool to make an occasional repair, you may not need to spend the extra money for the high capacity battery. On the other hand, if you are using that same tool as a professional carpenter, you will definitively want the high capacity battery.
Hopefully, this has helped de-bunk the confusion about cordless power tool batteries for you. Of all the factors involving the purchase of a cordless power tool, the batteries are the most important single factor.
Many cordless power tools are now sold as “bare bones” units, without batteries included, permitting the purchaser to make their own decisions on what kinds of batteries they want to buy. Also, since many handymen and craftsmen have multiple cordless tools, it is common to interchange batteries between tools (at least tools from the same manufacturer).
One last point I’d like to make, regardless of how much you use your cordless power tools, it’s always a good idea to invest in an extra battery, as this is the one part of your tool that is most likely to fail.