Cordless power tools succeed or fail on their batteries, and Milwaukee is a power tool manufacturer that claims to have developed proprietary battery technology that beats everything else on the market in a big way. Figures like 40% longer run time between charges and 20% more power than the best competing batteries are being quoted, and this sounds like typical advertising hype to me because those gains are so huge. That’s why I put these numbers to a very rigorous, real-world test.

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 identical tool to test two batteries – one was Milwaukee’s regular 18-volt and the other a RedLithium 18-volt. To make the test most accurate, I ran each lag bolt in and out of a 3/8-inch diameter pilot hole 10 times, before moving onto a new hole. More drives than this and the holes got too large to maintain consistent friction. Fresh holes mean tough driving, and that’s what I wanted. To measure claims for increased power, I also timed how long it took to drive each batch of test bolts from start to dead battery.

To ensure consistency, I ran the test for each battery twice, after a full charge and recharge, and after the impact wrench itself cooled down. In the end I discovered that not all commercial claims gild the lily. In fact, Milwaukee has understated RedLithium performance based on my lag bolt test results. Work completed on one charge was a whopping 73% greater for RedLithium, while driving each screw an average of 18% faster. Be sure to see a video of my test in action.