Ask the Builder: Cordless tool power depends on battery

DEAR TIM: It seems every month there’s a new cordless tool. The claims about power and run time seem unbelievable. Before I start investing heavily in cordless tools, I’m wondering if you can weigh in. Are they advancing to where they really can perform equally with a corded tool? What’s the latest information you can offer about lithium-ion batteries, and what separates a good cordless tool from a great one? – Mike S., Fall River, Massachusetts

DEAR MIKE: Just a couple weeks ago I attended a tool conference hosted by a power tool company that’s probably the leader in cordless power-tool technology. They make amazing batteries and tools. I had dinner with the engineer in charge of their entire lithium-ion battery division and had an extended one-on-one discussion about batteries.

I asked him all sorts of pointed questions about where the industry is on the power and technology curve with lithium-ion. I also asked about the differences between battery packs that appear to be similar. I discovered there are significant differences between battery packs from one power-tool manufacturer to another.

Most cordless power tools have a squarish plastic battery pack. Inside this case you’ll discover multiple small cylinders that contain lithium-ion. These small cells in shape and size resemble a five-dollar roll of dimes you might get from the bank. A simplistic explanation of battery power is this: If you want more voltage, you need to have more of these cells connected to one another in the large black plastic case.

However, the reality isn’t that simple. As you might expect, not all lithium-ion cells are the same quality. Moreover, the way the cells are packed inside the case and connected to one another is not the same. If the cells are not protected against water and shock, the power pack can become useless if left in the rain overnight or dropped a few times.

To answer your question about the power claims, I can tell you that the tools I tested will satisfy those claims. Believe it or not, it’s possible to have a cordless tool last all day on just one or two batteries. It’s all a function of how much work the average person does with a tool in a given day.

If you plan to have the tool on for eight hours straight, the batteries will not last. Most contractors don’t work this way. They use their power tools for short bursts of time. For example, an electrician may use his drill to bore holes in 20 or 30 wall studs and then set the tool down while he runs cable through the holes.

I discovered a few magic ingredients that are making the new cordless power tools faster and more powerful than corded tools. Not only are lithium-ion batteries better than ever, but the motors inside the best tools have better parts and are better engineered. The real secret sauce is a third ingredient you probably never thought might be in a cordless tool: micro-electronics.

For example, in the best tools there are tiny computers that allow the tool to communicate to the batteries and vice versa. If the computers sense you need more power to cut a thick board or drill through dense lumber, they allow more power to pass from the battery to the motor. If the tool senses it’s not under much load, the computers become stingy with the power and only allow enough into the motor to satisfy the demand. This preservation of the power allows the cordless tool to run for hours and hours.

One of the questions I’d ask about when you’re looking at cordless tools is what happens if rain gets onto or inside the lithium-ion battery. I saw a battery pack that was ruined in less than 24 hours because water had filled the pack. This water caused significant corrosion that rendered the battery useless.

The battery packs I saw from the tool company that sponsored the event had drainage channels and holes that allowed any water to exit the battery. The micro-electronic components were also coated with a water repellent so they would not short out if water got on them. This kind of engineering helps preserve your investment as you migrate to cordless tools.

I did hands-on testing of quite a few new cordless tools and can tell you that if I had been blindfolded, I would have sworn I was using a traditional corded tool that ran on standard 120-volt current. In my opinion, the days of corded power tools are numbered.

I feel it’s safe for you to buy cordless tools as long as you do your homework. My cardinal rule when buying any tool or building product is to use price as a barometer. The best tools and products almost always cost more because they contain better parts, better technology and better engineering.