Ni-Cads could work, but Li-Polys are a big danger. With gel cells and car batteries, you can have a short at the pad while holding the launch button and nothing too bad will happen unless you hold it there all day. With Li-Polys will fail catastrophically when subjected to this kind of torture for more than a fraction of a second, (and we know what happens when you get a misfire: "Oops, didn't work. Let's hold the launch button in for 10 seconds, then see what's wrong.") A melting/venting/burning Li-Poly is the last thing you want a couple inches from your hand.
That's not correct. Lithium-ion and lithium polymer batteries are quite safe as long as they are not overcharged, physically damaged to the point of developing internal shorts, and are properly packaged.
Lithium-ion batteries (the ones in your computer) and Lithium Polymer batteries (the ones in your cell phone) are a bit more robust, and less hazardous, than you portray. If they weren't, you couldn't have them in your computer or your cell phone.
The big danger with lithium batteries is due to overcharging. Most lithium batteries will be damaged if they are charged to more than 4.2 volts per cell. This will overheat the batteries and in the case of Li-ion batteries, the casing can rupture, and because the electrolyte used in a Li-ion battery is flammable, it can catch fire. Li-poly batteries do not use a flammable electrolyte, however the plastic casings can overheat, rupture and burn if they are overcharged.
Lithium-ion and lithium polymer batteries themselves get warm and even hot when they are discharged at a high rate, however the hazard is a heat burn, and not a flame. The flaming laptops that you saw on youtube were due to a manufacturing flaw inside one of the lithium ion batteries that created an internal short inside an individual cell which caused the electrolyte to catch fire, and then set off the rest of the batteries and the laptop. This will not happen with lithium polymer batteries since the electrolyte is not flammable, but it is possible to get a severe skin burn from an internally shorted lithium polymer battery.
If a wire accidentally shorts a high capacity Lithium-ion, lithium-polymer, and even a NiMH, NiCad or Pb-acid battery, the wire can become very hot and ignite the surrounding container. (After all, this is how igniters work.) This is a very real hazard and is the reason why you are not allowed to carry loose, unpackaged batteries of any type on an airplane.
Bob