There are a lot of videos on both sides of this issue out there.
The Model Airplane people (which I am one of) have been dealing
with this for a while. The products this person is dealing with
have been proven safe when used properly. That includes, minimize
the number of batteries being charges at one time, charge at a
slow 1C maximum rate, charge outside, preferable on concrete or
gravel, and don't use puffed batteries. I have seen Lipo and other
similar types of battery burst into fire. They are difficult to
put out and best let them burn out.
Let's be clear. These products do NOT contain the fire/burn. They
are designed to minimize it. There are dozens of examples of
people charging in their cars, only to have their cars burn up due
to a burst battery.
In my experience, the people with the most problems with their
batteries either, 1) charge to fast, or 2) don't wait until the
battery has cooled before charging; thus abusing the battery.
My recommendation is to keep them in a metal box (Ammo can, drill
a couple of holes in the top for fire vent if necessary), with
only a few batteries per box, store the box on a concrete surface
(such as in your garage), and away from other flammable materials.
After many years of Radio Controlled flying and dealing with
these batteries, I have yet to have a problem as I follow my
There, my 2 cents.
Bob Ackerman, N6VZO