When charging, you are also activating circuitry within the car, which can draw several hundred watts - This draw is the same for L1 or L2, but since L2 is more than twice as fast, that draw is for much less time

One of those losses is that you are powering the DC to DC converter to charge the 12 volt battery and that converter is running all the time you are charging, regardless of whether you're using L1 or L2. I don't know the exact figures for the Volt, but with my Mitsu, the associated 'losses' to all other circuitry is between 500 and 600 watts, largely due to the DC to DC converter. Assuming the Volt is similar, that means for L1 charging at 12 amps, (1440 watts) 500 of those watts are not going to charge the traction battery, so it would only be getting 1,440 minus 500, or about 940 watts. When charging L2 again at 12 amps (2,880 watts) the traction battery is getting 2,380 watts.

2,380 watts is __way more than twice__ as much as the 940 watts it's getting when L1 charging. Again, I'm not sure what the losses are for the Volt . . . . maybe they are less, but they are still there and they are the same for L1 and L2 and since L2 is more than twice as fast, you're not 'wasting' those watts for nearly as long when using L2

Don