More and more of the power tools on the market today are cordless tools. The ability to use the tool anywhere, without having to run extension cords, makes these an attractive option for professionals and do-it-yourselfers alike. Whether for small repair jobs or major construction, cordless tools are gradually taking over the power tool market.
The only problem is that sorting out all those batteries can give you a headache. Every manufacturer seems to tout their choice as the best on the market, which is nothing more than you would expect of them. Still, that doesn’t provide much help when trying to decide what to buy.
When picking battery-operated tools, you’ve got to know what the battery specifications mean. Basically, there are three things to look at:
- Battery material
- Battery voltage
- Battery capacity (amp-hours)
There are three different materials that are used for making rechargeable batteries. Understanding each one’s strengths and weaknesses will go a long way towards helping you pick the right battery for your needs.
- Nickel Cadmium (Ni-Cad or NiCd) – These are the oldest of the three types of common rechargeable batteries. NiCd has been in use since the 1950s. They are still the most economical, but that is changing rapidly as Li-Ion battery prices are dropping. These batteries can last up to 1500 charge cycles. However, they don’t hold all that big a charge. Recharging of NiCd batteries can take an hour up to 3-1/2 hours. They also have a “memory” so you can’t partially charge them.
- Nickel-Metal Hydride (NiMH) – This was the first replacement for the NiCd battery. They have about a 50% greater energy density, so they don’t have to be recharged as often. However, they don’t handle recharging well, lasting only 1/3 the recharge cycles of NiCd.
- Lithium-Ion (Li-Ion) – We could call Li-Ion the new kid on the block, as they are the most recent type adopted for power tools. The really great thing here is that these batteries have double the energy density of NiCd, meaning that you can do twice as much work on a charge. They also charge much quicker, with a typical recharge time of 30 to 60 minutes, depending on the battery type.
One other important difference between NiCd and Li-Ion is the way they discharge. NiCd discharges gradually, with the voltage dropping slowly as the battery discharges, much like an alkaline battery does. This means that a drill or saw will gradually run slower and slower, until it reaches the point where it isn’t usable any more. Li-Ion on the other hand holds its voltage throughout the life of the charge, and then drops off suddenly when the battery is discharged. A lot of people have complained about this, but once you get used to it, it’s actually better.
Battery voltage is the second important indicator. The first cordless drill I bought had a 7.2 volt battery; now they typically have 18 volt batteries. The battery voltage gives a rough indication of the power that the tool will have. Motors which run off of higher voltages can generally produce more torque, which of course, equals more power. So, if you are needing power, you’re better off buying the power tool that uses the highest voltage batteries.
The battery capacity is the least understood of the three important specifications. Capacity is stated in amp-hours (aH). That literally means how many hours the battery can provide power, if it is providing one amp of power constantly. So, a 1.5 Ah battery can provide 1 amp of power for 1-1/2 hours. Of course, most tools require more than one amp of power, so in the case of a saw that needs three amps of power, the battery would power the tool for 30 minutes before needing recharging.
Some manufacturers offer two versions of their rechargeable battery systems; a “slim line” battery and a “fat pack.” Typically, the fat pack will hold twice the capacity of the slim line, allowing you to work twice as long between charges. Of course, the battery will also take correspondingly longer to charge.
With these three specifications in mind, you can know what you’re looking at when you start comparing different power tools from different manufacturers. That will help you to make sure that you’re really comparing apples to apples, instead of apples to oranges.