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Expert Tool Tips
ExpertToolTips.com by Tim Carter, Author of the Nationally Syndicated Newspaper Column Ask the Builder


Drills : Cordless Drills      E-mail to a Friend    Print this Page

Cordless Drill Batteries and Fire Hazards

Cordless drill batteries can catch fire. A dead short across the battery terminals can start the fire. Do not store the battery around loose pieces of metal. If the battery came from the manufacturer with a protective cap, use it when the battery is not in the tool.

Cordless drill batteries, actually any cordless tool batteries, represent a significant fire hazard in your home shop, garage, truck or car trunk. These power sources, when charged, have stored energy that can arc and start a fire if the right conditions exist.

Most people are oblivious to these hazards, as they have never seen a battery start a fire. But recently, laptop-computer batteries have been in the news, because they have spontaneously combusted and started several fires.

Electrical fires happen every day, and many are related to high voltage (120 - 240 volt) found in homes and businesses. But you can get sparking and arcing at very low voltages. The arcing and sparks produced by a 12-volt powerful car battery are impressive. They can easily start a fire given the right conditions. Think about the stored energy in a fully-charged 18, 24 or even 36 volt cordless drill battery. It is impressive to say the least.

To start a fire with a cordless drill battery, all one has to do is short out the contacts on the battery.
  • NOTE: Do NOT do this to see what happens. It is very dangerous, and can harm yourself or ruin the battery.
A dead short happens when any piece of metal touches both battery contacts at the same time. You will have to work to do this, as the battery manufacturers try to separate the contacts and recess them to make it hard for this accidental arcing to occur.

But what happens if you drop a cordless drill battery into a box and then start throwing scraps of metal, nuts, bolts, nails, screws, etc. on top of the battery? It's possible for these different pieces of metal to touch one another, and for two of them to be in contact with each of the battery contacts.  This direct metal pathway would complete the circuit, and the battery's stored energy would rapidly course through the metal.

In normal usage, a cordless drill battery has the drill motor between the battery contacts. The motor provides resistance to the flow of electricity. This is a good thing, as the movement of electricity through the battery is slow. But when there is little or no resistance between the battery contacts, as in the case of the short I described above, the flow of electricity through the battery is fast, very fast. This rapid movement of electricity through the battery causes increased friction and heat which can cause the battery plastic to overheat and actually catch fire.

The batteries for many of my Bosch cordless tools have fantastic plastic protective caps that minimize or eliminate the possibility of short circuits and arcing. If you have caps like this, use them when the batteries are not inserted in the tool. If you don't have caps, try to fashion some using some form of durable plastic.

Avoid using adhesive tape to protect the battery contacts. The adhesive residue can foul the inside of the cordless tool, as dirt can be attracted to any sticky residue that might be left behind when you remove the tape. The dirt can collect on the electrical contacts inside the tool or on the ends of the battery.
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