Thanks Tim! Sorry to be so serious about all this, but lithium batteries are starting to be used by cavers now. (If you use a Sten light you most likely have lithium ion batteries.) Just wanted to make sure the people who begin to use these batteries fully understand the dangers they pose. You can not treat these batteries like other batteries you use. Lithium ion batteries do not tolerate the abuse that people are able to throw at other batteries and get away with. Instead, they bite back.
Before I built this lithium ion battery pack I did an extensive amount of research. As long as you treat these batteries with respect, handle them like you are supposed too, they are fine. People who build their own lithium battery packs often push their lithium batteries beyond their limits. This can create damage inside the battery you can not see. Minutes to hours later a battery can decide to spontaneously short circuit itself and go into a runaway reaction. The natural result you see is the battery spontaneously exploding or catching on fire. Even if you do everything you are supposed to do, they can still spontaneously catch fire due to a manufacturing defect. Think the Sony Battery Laptop recall.
The fire resistant document safe has a hydrated mineral in the walls. When heated to high temperature it release the water and keeps the documents inside from burning. If lithium batteries are put inside such a safe and catch fire, it does the same thing, contains the fire inside, absorbs the energy, and prevents the fire from escaping. This safe is not that big or that heavy. I only use it to store my batteries in my truck while out caving. While in the cave I transport my lithium battery in a waterproof pelican box.
If you are interested in another layer of protection, we can take a tip from the RC community. They store their Li-Poly cells in a Sentry fire document box. I believe they are around $25 at Target and Wal Mart. Holes are drilled into the box to allow rapid gas venting. The box is kept in a safe place with the vent holes pointed away from combustible surfaces.
The Brinks cash box has also been used. Once again vent holes are needed because the rapid gas build up will pop the latch and the lid will fly open. The Brinks box is not insulated, so it must be kept off of combustible surfaces as well as the vent holes pointed away from such surfaces. Partitions can be utilized inside the box to try to isolate sections, but the boxes are not that expensive so people are purchasing several, spreading out their cells amongst several boxes.