http://www.youtube.com/watch?v=WX-_azD2 ... re=related
You might wonna look at the above video before it dissapears like their website.
It's a 400+ HP electric car using Lifepo4 cells. First they used Headway cells, now i think it's got 300 (100S3P) 20Ah A123 pouch cells. Lipo is more expensive and won't last as long as Lifepo4 but will give more instantanious power then the above. It's basically all up to how much you want to spend on it.
My experiance + long term research on cell discharge;
Lipo cells can take up to 100C for 2-3 seconds. 70C for 5 seconds. 30C for 50% capacity
Lifepo4 cells can take only 30C tops for 2-3 seconds, 10C for 5 seconds. Probably keep it at 2C for 50% capacity
Charging wise, i don't exceed 5C on Lipo but am confident they can do more. Lifepo4 is supposed to charge even faster and 10C is being done in RC applications.
With regards to cell balance. I think that even Nimh packs deserve a balance function and certainly it's well worth the effort to do this with Life or Lipo to be safe and enjoy a long battery life with peak performance.
How much power can the generator deliver? I think you would only need about 15-20KW to be able to maintain 70mph long distance. If you want to start and stop a lot without regen then obviously you could want more. The battery pack is just there as a giant capacitor.
EDIT; new website for the BMW; http://www.rimac-automobili.com/evaluat ... vehicle-11