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
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.