And maybe being sold a ruined one that you don't realize has been ruined until after you bought the thing and discover the moldy carpets, the rust under the dash and the endless electrical problems caused by water getting into the wiring.

When a device is flood-damaged, there's more to worry about – such as a spontaneous fire triggered by water contacting the materials within the battery.

This can – and does – happen for basically the same reason that Luke was able to destroy the Death Star in the original Star Wars movie. Luke knew if he managed to send a missile down a ventilation duct that led to the Death Star's core, he could blow it up. A device – the proper name for these battery powered things that look like cars, sort of – also has a vent. And that is how the water can get in when the vehicle ends up in water that's high enough to reach that vent.

Then it's Oscar Meyer Weiner (or S'mores) time.

But maybe not immediately. It all depends on when the water get into contact with the battery pack's insides. That may not happen at first.It might take a little time to work its way into the critical areas. But, regardless, water (especially salty/briny water) is extra-bad news for devices and those in the vicinity of one, if a fire suddenly erupts. In italics because that is exactly what can and does happen with device batteries. They just ignite – no need for a spark.

Such fires are hard to predict – or prevent because they literally just happen.

This is an important difference vis-a-vis vehicles with engines that are not devices, because with those, there must also be a spark in order for there to be fire. So, there must be two things – leaking fuel and a spark – present in order for there to be a fire. If one is missing, no fire. This is why a vehicle with an engine – and a gas tank full of fuel – will not erupt in flames unless there is a flame (spark) even if the fuel is spilled/leaking from a damaged gas tank. This is a huge safety advantage as well as a peace-of-mind advantage in that there is almost no chance a parked car will spontaneously catch fire – unless someone puts a rag in the gas tank filler neck and lights it on fire.