To understand why water doesn't bother the batteries or the motor in an electric car, first consider the fact that every car you've ever driven has had an electrical system. It operated at much lower voltages, used a different kind of battery and served a different purpose from the system in a hybrid car, but the principle is the same. All cars have batteries and electric systems, yet they don't short out or shock anyone in the rain. Even if you get water on the battery terminals, it generally just causes corrosion, not an immediate catastrophic effect. In fact, in several models, notably certain Chrysler vehicles, the 12-volt battery is mounted behind the front tire, near the bottom of the car, where it is frequently exposed to water and other road debris.

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In the event that water does actually get inside the shell, there's still not much to worry about. The nickel-metal hydride batteries used in current hybrids and electric cars are maintenance-free sealed cells, so nothing gets in or out. The chemicals inside are designed to form a gel, so they won't spill even if the batteries are ruptured in a crash. Under normal operating conditions, it's pretty much impossible for water to come into contact with the batteries themselves. The high-voltage lines that carry the current are similarly protected and insulated.

The bottom line -- don't worry about dodging puddles in your Prius.