That would be easier than making the not exploding gas tank. Many people are killed every year when their gas tank explodes or catches fire, from such trivial things as driving over a loose manhole cover. Gasoline is a very volatile and extremely flammable liquid (not to mention cancer causing fumes). Presumably the fuel used in a Series Hybrid would be a much less flammable / explosive diesel. The developers of the Tesla don't seem to be worried about that point, and it is a trivial problem compared to the hydrogen fueled vehicle (5,000 to 10,000 psi fuel tank) hydrogen economy crap that is being massively pushed by the pro-oil bush administration, Big Auto, and Big Oil interests.

Your statement is undoubtably based on the recent Li-Ion battery pack fires in Laptops. It is invalid to blindly extend this to automotive type batteries, which are a totally different application. Laptop batteries, are made as cheap as possible - probably the designers have less than a $25 budget per battery - protection systems would add weight and cost to a very limited size / cost system. It is easy to prevent these internal short circuits, (which occur in something like .00001% of batteries produced) with internal fusing or thermistor monitoring, not a difficult problem when you have a dedicated energy storage system, as you would have in a vehicle battery pack.

Also, this so-called series-parallel hybrid vehicle is really a parallel hybrid vehicle, and quite a different concept than I am talking about, which is a pure electric vehicle with generator option, such as found on:
http://www.fevehicle.com/services.html