If the supplied cord has "properly" sized power conductors (for the 40-amp circuit), the power (IxIxR) losses in the cord, though certainly measurable, should be fairly insignificant.
Most installations will have cords much shorter than 50 feet, I suspect. I have no answer yet (from AV) on what the "available" cord lengths will be. I would guess that 15 to 25 feet would be more typical.
However, there are limited-access cases, like mine, where at least 30 feet will be needed, and 50 feet would help.
Also, the cable might be detachable from the home-version of the EVSE box (as a simple way of meeting the strain-relief safety requirement on the EVSE), so a short cord might be supplied for "typical" use, with the option to buy an "expensive" interchangeable longer cord.
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