I reckon the future battery will be a super cap/battery combo. As previously pointed out , they both have their advantages and disadvantages. There's a company ( In Estonia I think ) that is doing one of these. As long as they can make them small enough I reckon they will be the go.
I have read that you can only harvest about one third of the regen power with a normal ev battery pack. With a super cap you can grab nearly all of it.
Some pretty obvious benefits of a combination arrangement I reckon.
