The main inverter is going between motor voltage and pack voltage, and depending on the car can handle regeneration at upwards of 60 kW (Teslas) to 265 kW (Porsche Taycan).
The cable that is putting 30 kW into the battery? It's the same one that's designed to conduct 80-110 kW from battery to motor in your Leaf.
Skeptical of what exactly?
Even if the benefits of regenerative braking were zero, electric vehicles still make sense for delivery vans. They have known ranges, usually less than 100 miles and the reduction fuel and maintenance costs will be huge. This is why there is so much interest in the Tesla semi and other similar tech where regenerative braking has nearly little effect on milage because the vehicles aren't stopping often.
But existing driving data suggests there will be some non-zero effect on efficiency through regenerative braking so I'm not sure what the point here is.
https://youtu.be/KAIzAlgHF2E?t=57s
It measures regenerated Wh. In my case it was in increments of 30Wh.
How thick is the cable taking the 30KW and putting it in the batter, when the on-board charger on that thing only puts out 3.3KW?
As thick as the one putting 100kW into the motor I guess, so at 300V - not very thick.
You see the traffic slowing down, foot off the pedal, regen starts and the car slows down. Traffic gets going again, push the pedal.
If you drive a hybrid/PHEV/EV like you would an ICE, it won't be economical.
And I'm pretty sure your meter is measuring KW, not Wh. Regardless, I question its accuracy in our Leaf. How thick is the cable taking the 30KW and putting it in the batter, when the on-board charger on that thing only puts out 3.3KW? And maybe the answer is, "as thick as your wrist, but it's very short"), dunno, but color me skeptical.