you probably want to look into supercapacitors for bursts, the losses from charging/discharging two battery banks hurts my head.
Electric double-layer capacitor - Wikipedia, the free encyclopedia
In fact being able to manually manage the charge on a bank of super capacitors would be a cool thing:
"I have to slow down over there, better leave the capacitor discharged to soak up that stop with the regen".
"I have to slow down over there, better recharge the battery from the capacitor so I can soak up that stop".
"I'm going to need to accelerate quickly here, better charge the cap from the battery a bit"
It is all situational but could be very efficient if properly managed.