I decide to do some reading. We probably see Chemical to Mechaincal+heat (work and heat) efficiencies og engine/work, but KE to electrical on regen brake is still kinda new.
https://www.sciencedirect.com/topics...0or%20severely.Regenerative braking allows the range of the EV to be extended; however, the efficiency of capturing this energy is reported to vary from 16% to 70% (Boretti, 2013). The reason for this significant difference in efficiency will depend on the driver's style of driving whether they brake gradually or severely. Furthermore, temperature of the system and outside ambient temperature affect the efficiency greatly. The driving technique of the driver is a considerable factor when calculating the efficiency of the regenerative braking system. Friction brake pads are installed in the EV to allow for more rapid braking as opposed to slow braking with the regenerative braking system. The utilization of the friction brakes results in the efficiency of the regenerative system to vary.
Chemical energy ->Kinetic Energy -> electrical energy from regeneration would be substantially lower.