Understanding Cordless Tools

Demystifying volts, amp hours, and types of cordless tool motors.

- Collin Knoff

More and more, cordless tools are becoming everyday fixtures in the woodworking shop. The most common of these is the drill, which you can see broken down to the right. Most cordless power tools have the same basic components, though, so once you understand how one tool works, you'll be well on your way to understanding them all.

Volts vs Amp-Hours

The two numbers that appear on the sides of most tool batteries are volts (V) and amp-hours (Ah). So what's the difference? If we were to use a car as an analogy, volts would be how much horsepower/torque your engine has, while amp-hours would be the size of the gas tank. (Before any battery engineers write us letters explaining how inaccurate that is, remember we're a woodworking magazine, not a scientific publication.)

When comparing the different levels of voltage, it's important to remember that this reflects the peak available power, not the amount of power a tool is constantly using. That's why you don't see any normal drills with 40V batteries—all that power just adds unnecessary weight to the tool. It's also the reason a 12V drill can complete 90% of the tasks of an 18V one. So, when looking at the difference in voltage between tools, higher isn't always better.

Amp-hours is a term that is a bit more misunderstood in the world of batteries and battery health. Most people only look at the voltage a battery provides and completely ignore the other number next to it. However, the length of time a tool will run is often just as important as how much power it has. A 1.5Ah 20V battery is going to run out of juice much faster than a 3Ah 12V battery under normal usage. Not only does this interrupt your work, but it can also shorten the life of a battery (see