Cordless power-tool test
Cordless power tool performance ultimately comes down to battery performance, and last year at this time claims by one tool manufacturer about their batteries sounded pretty boastful. Figures like 40 per cent longer run time between charges and 20 per cent more power than the best competing batteries were being quoted by one manufacturer, and that’s why I put these numbers to a rigorous, measurable, real-world test.
Milwaukee is one of a handful of international power tool manufacturers, and their RedLithium batteries were the source of all the talk. To test their big claims, I used an 18-volt impact wrench to drive 1/2-inch diameter by 6-inch long lag bolts into and out of predrilled holes in the side of a red oak test log as many times as possible on a full charge. I used the same power tool to test two batteries — one was Milwaukee’s regular 18-volt lithium-ion battery, and the other was a RedLithium 18-volt. I also kept track of how long it took to drive each batch of test bolts from start to dead battery, to gain a sense of tool speed.
Not all tool batteries make tools run at the same speed, even when the batteries are supposed to put out the same voltage. My tests have shown that a so-called 18-volt tool battery regularly outputs 21 or 22 volts at rest. How much voltage drops under load varies quite a bit from one battery type to the other, and this voltage drop determines how fast a tool operates.
One of the things that surprised me was just how hot the lag bolts became during my test. After 15 or 20 drives into and out of the wood, the entire lag bolt was smoking and way too hot to touch. The oak log I used was still fresh enough to contain lots of sap, which actually boiled away vigorously around each bolt as it went into and out of the steaming wood. Ultimately, all this energy comes from the battery pack driving the tool, and it’s visual proof that today’s cordless tool batteries hold a lot of energy. When the bolts got really hot it even caused audible puffs of steam to come out of the hole as the metal pulled away from the wood.
To ensure consistency, I ran the test for each battery twice, after a full charge and recharge. I don’t know if an super hot tool would interfere with fair results, but I also let the impact wrench cool down between test sessions, just to be sure.
The bottom line is that not all advertised claims exaggerate. In fact, Milwaukee has actually understated RedLithium performance based on my lag bolt tests. Work completed on one charge was a whopping 73 per cent greater for RedLithium than regular lithium-ion tool batteries, while driving each screw an average of 18 per cent faster.
Another legitimate tool advance that’s showing up across all tool brands is brushless motor technology. This is a simpler, more efficient way to build the electric motors that power drills, impact drivers and other cordless tools, and I have no doubt it will become main stream within the next two years. More on this in future columns.
Technology doesn’t usually stay proprietary for very long these days, but RedLithium batteries are still leading the pack right now, even a year after my tests. I use a wide variety of cordless tools regularly in the course of my work, and so far I haven’t found anything that rivals RedLithium. As the tool manufacturers scramble to keep up, tool users are the big winners, especially if you’ve take the time to figure out which technology is currently the best, then get it into your toolbox.