Understanding Cordless-Tool Batteries
Misused batteries die young. Replacements are costly. Here's how to get the longest life from your batteries.
Synopsis: This article explores why higher-voltage cordless tool batteries have shorter lives than lower-voltage batteries, provides a brief overview of current battery technology, and explains how to optimize the life cycle of your batteries so that they last longer.
Three months ago, I carried a boxful of one-year-old 14.4v batteries into my local tool dealer’s service center. The service technician tested the batteries and confirmed what I knew: Those batteries would no longer take a charge. He couldn’t tell me why they lasted for just a year, which only added to the aggravation of buying six new batteries for $60 each.
The batteries in my old 9.6v tools lasted for years, driving thousands of screws. However, I’ve noticed that 12v, 14.4v and 18v batteries degrade faster. After about one year, they don’t deliver their original run time or torque, regardless of the claimed amp-hour rating. (Amp-hour is the industry’s standard measurement of the electricity that a battery can store and release on demand.) Other carpenters had similar complaints.
To learn what was going on, I spoke with representatives from Makita, DeWalt, Porter-Cable, Bosch, Milwaukee and Hitachi, as well as Sanyo and Panasonic, which manufacture most cordless-tool batteries.
The manufacturers confirmed what I suspected: Higher-voltage batteries have shorter lives. Manufacturers estimate battery life along these lines: 1,000 to 1,300 charges for a 9.6v battery; 800 to 1,000 charges for a 12v battery; 650 to 800 charges for 14.4v battery; and 500 to 800 charges for an 18v battery
Battery life isn’t wholly dependent on voltage ratings, though. How a battery is used also affects its life. What follows is a summary of my conversations with the manufacturers.
Heat is a battery’s worst enemy
My crews use today’s high-voltage cordless tools for harder tasks than the light, occasional duty we expected of 9.6v tools.…