I think that NiMH batteries are also not that far behind dynosaurs ... didn't they fall out of favor for cordless small hand tool use some time ago? Some form of Lithium seems to be where it's at nowadays in contractor cordless hand tools (... and of course for electric vehicles, too).
Those energy content versus battery size versus battery weight specs are beyond superb.
NiMh is, in a special version, used for the Prius.
Only problem is getting a hold of used Prius batteries are difficult and then having to fiddle with a 280V deal.
The Ford Escape Hybrids are powered by Sanyo cells, are also NiMh and easier to get.
Lithium I am a bit queasey with --- because of the fire risk and the need to have temperature monitoring and sensing, plus cooling and other things.
Since this is a hobbyist application, it always comes down to what one can salvage at the scrap heap from a busted car.