Anyone put thought into "reGen" braking add-on?

[mjp8081]

I have enough hills in my area (SF, CA) to make me wonder if anyone has tried to convert or add a circuit to collect power during braking/downhill and route it back to charge the batteries? Does anyone have any ideas about adding something like this to a somewhat standard eMTB/RC build? Thanks

 

[Hummina Shadeeba]

Already in there. Only like 6 or 8 percent though I think. Depends on the esc. Think the vesc has the most.