Math question. What is the equivalent energy in watts of 30 gals of gasoline? That's about, lets say, all it 200 pounds with the gas tank, pumps lines etc. So if we had a battery that weighted something on the order of 200 pounds and was about the size of a 30 gal fuel tank how many watts would it produce nearly instantaneously if it was all released very quickly.
Kinda like a gas tank catching on fire and burning vigorously until it was expended. I'll be fair and acknowledge that it is rare that there is an explosion. Usually just a big hot fire. However, batteries usually heat very quickly when internally shorted and produce explosive gasses that then explode. One big battery, or all the cells in the same container, would be a bad idea. My guess is that several batteries spread about the car would be safer, although more expensive.
The other problem is putting the fire out. Gas is fairly easy to extinguish. Cool it and/or remove the oxygen. An electrical fire on the other hand, usually burns until the current is cut off. This will present a new issue for fire departments. I have wondered about electric cars stored in a home garage for example. Insurance companies will quickly access risk if there is a perceived wide spread risk of electric cars burning down houses for example. This is becoming a question concerning solar systems on wood roofs as more and more homes install them. In both the solar and electric car question, insurance companies will begin to worry when the currently relatively small numbers become more wide spread and thus the ability to spread the isolated risk of these types of electrical systems is diminished by the rules of large numbers.
The bottom line is that a battery that can produce the energy density of gas will more than likely, be more dangerous than gas on several levels.
