No doubt that the Li-ion batteries have a greater power/density/weight capability than some of the not-so-old batteries like the nickel-metal-hydride ones. Funny, but Toyota sticks with those nickel ones for their Prius.
@gums
You might want to do a little research.
ALL Prius vicheles sold outside of North America feature Li-Ion batteries.
The US "pluck-in" version also featurs Li-Ion.