Regen braking

any electric motor or generator can be converted into each other. How to convert? But which conversion? You need to ask the right questions first, for you to get a correct answer. To give you an example, you can ask, how to convert your alternator as a regen? Since it is already a generator, it is already a regen. Just connect your crankshaft to the alternator when you brake, use engine braking, then you have regen. This alternator can be converted to a motor by adding a brushless motor controller that actually can turn the crankshaft, to run the aircon, or even move the car by engaging the clutch. You can run both in parallel. The alternator charger is primitive so you cannot get maximum charging at low speed. Use a charger like IMAX B6, to double the input voltage and output at a constant voltage with higher currents into the batteries. This is what is done by Tesla cars that have high regen braking. At low speed, the generator voltage is too low to charge batteries.