Beware The Cordless Tool Battery Charger

Bruce Bjorkman, from Cooking Outdoors with Mr. Barbecue, recently told me of a friend whose house burned to the ground as a result of a cordless tool battery charger catching fire. Doing a quick Google search, I found, to my surprise, that this is more common than I would have expected. Based on the articles I read, I’ve compiled a list of six suggestions for safely charging power tool batteries:

1. Don’t ever leave batteries charging overnight.
2. Put battery chargers on a switched power strip that also runs something you wouldn’t leave on when not in the shop, like a radio.
3. Put a smoke detector in your shop, near your power tools.
4. Check to see if your batteries or the tool have been recalled.
5. Stop using formerly silent chargers if they begin “singing” or whining.
6. Don’t trust the user’s manual, even if it says it’s ok to leave batteries charging.

There is one common misconception that I’d like to clear up about the proper way to charge cordless tool batteries, now that the safety consideration has been addressed. Because early NiCad batteries were first used in low current devices like cordless phones, they developed a “memory”, and after a while simply wouldn’t hold a charge. The solution was to periodically leave the phone out of the charger, letting the battery discharge fully, and then recharge it.
As consumers, we developed a memory as well. Many folks think that the proper way to treat a cordless tool is to fully discharge it before putting it in the charger. This can actually damage the battery. Instead, you should stop using a battery as soon as you feel a substantial decrease in power from the tool. The other consistent recommendation I found when doing the research was to let the battery rest and cool down before putting it into the charger and this suggested charging technique was the same regardless of the type of battery.

Finally, there is a lot of confusion surrounding the different types of cordless tool batteries in use today. There are basically three, Nickel Cadmium (NiCad), Nickel Metal Hydride (NiMH) and Lithium Ion (Li-ion). Lithium Ion batteries are probably the wave of the future for two major reasons:

1. They deliver comparable power in a much lighter weight package, and
2. They have a very long shelf life without losing a charge.

Lithium Ion chemical action produces about 3.6 volts per cell while all other common varieties, whether lead acid, alkaline, or NiCad, produce 1.2 volts per cell. This is why some of the smaller cordless tools only have a 4 volt battery. It’s not really a battery at all; it’s only one lithium ion cell. Technically to be called a battery, it must be two or more cells connected together.

And, the long shelf life is a very welcome characteristic of the Lithium Ion battery. A typical Nickel battery will discharge naturally, 15 to 20 percent in the first 24 hours, 7 to 10 percent the next day, and about 1 percent every day after that. Lithium Ion batteries will hold a nearly full charge for months, making them an ideal power source for cordless tools that don’t get used every day.