Re: Super capacitors are a good touch
"batteries simply can't take the charge as fast as a vehicle under braking generates it, so horrendous proportions of the energy are lost."
Supercaps are a logical choice, but they have low energy density, which is why they're not used in most hybrids/EVs.
Having enough supercap Joule capacity to handle converting the kinetic energy of a 1 tonne vehicle at 60km/h back to electrical potential when halting the thing translates to something around the 100-120kg mark (and supercaps are NOT high current devices, so other issues come into play too)
I'm aware of one hybrid design (a passenger bus) which dumped energy from the regenerative brakes into the cooling system, only storing about 1% of the regenerated energy. It saved on brake wear but caused overheating issues in summer. (FWIW, trains tend to do this too - regeneration energy is usually dumped into resistor packs on the roof instead of putting it back into the grid as doing so results in unpredictable loads which are nearly impossible to regulate without extremely complex and expensive control systems - but it saves mechanical wear on the brakes.)