[samwichse]

Originally Posted by PaleMelanesian

This one happens to be true. There's a reason today's hybrids are using the problematic many-little-batteries-strung-together format. They are unable to legally use larger NIMH's.

I know, it's Wikipedia, but with lots of external references.
Patent encumbrance of large automotive NiMH batteries - Wikipedia, the free encyclopedia

The patents are due to expire soon, but advances in Li-Ion chemistries will make it largely irrelevant.

They're using many smaller NiMH cells strung together instead of fewer, larger-format cells because NiMH has a low cell voltage (~1.2V nominal). Using larger cells wouldn't get you more voltage, just more Ah. This could deliver more amps, but then you would need increasingly huge conductors everywhere to deliver any reasonable amount of power. Which makes everything FAR more expensive.

For instance, a gen 2 prius has 168 6.5 Ah cells in a series making 201.6V. That's a 1.3kwh pack. It can pull about 28kw from that pack. That's 139A (peak, though).

Now say you have 65Ah large format NiMH readily available (10x the capacity in one cell!), so you put in 1.5kwh of those for the same weight and volume (it's slightly larger since you don't have as much packaging/interconnect). Now you have a 19 cell, 22.8V traction pack. That pack is going to have to deliver over 1200A peak. Those conductors will be huge, that motor is going to be huge, and all that mass of copper is going to cost $$$. A low voltage pack is only economical for mild hybrids. IIRC Hyundai sold one for a couple years in Europe with a 48v pack, but it could just supply a bit of motor assist and stop/start functionality.