Just a little napkin math, a 200 HP engine (which is about what the Ford 3.3L makes at peak torque of 4000 RPM) makes about 149,000 Watts of power. So, assuming lossless charging, which I know is not the case, you could add about 75kWh to a battery in 30 minutes.
Now, I know there are lots of things at play here and this is more of an ideal calculation, but if you cut everything in half, you add 75kWh to a battery in 60 minutes. In our Mach E, we can drive over 200 miles on 75kWh.