The plug-in hybrid Prius has Li-ion, the rest have NiMh. The Nissan Leaf and Chevy Volt have Li-ion so best not to park next to them...!!
The energy density of those cells is less than the ones we use, so that helps. They don't cycle them from fully charged to fully discharged like we do so they can prolong the life of the battery. And you can't order them through the post!
I wonder why most of the mail order shops in the UK continue to offer Li-Pos if this is the rules? Strange...