Early LiCo laptop and hobby batteries were very light weight but were dangerous. The 787 early system designs were certified 5 years ago before the adoption of newer, safer battery chemistries. The new LiFePO4 cells such as the A123 Amp20 cells or the large cells from GBS or Calb are very safe for automotive use. Of course, any 3-400 volt battery capable of 1000 amps can weld metal and light carpeting and upholstery on fire if the electronics get shorted from salt water or a collision. It's not the battery on fire as much as the wiring and materials inside the car. I'm sure the battery in the Volkswagon will be one of the more modern and safer types.
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Here is a video from an Ebike builder trying to destroy an Amp20 cell including shooting a hole through it and chopping it with a hatchet.
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