These cords have No. 6 wire in them and that, with the lowest grade of insulation (60 °) is rated for 55 amps. With the Gen II mobile charger plugged in the vehicle will draw 32 Amps. No. 6 has resistance of 0.49 Ω/kft and a 50' cord has 100' of wire in it (out and return) for a total of 0.049 Ω. At 32 A voltage drop, for the single extension cord will be 1.568 V and power dissipation 50 W. Note that the cord is intended to be used in a 50 Amp circuit in which case dissipation would be more than twice this at 122 Watts. Plug two end to end and the voltage drop doubles to 3.136 V as does the power dissipation but note that the total power dissipation is less than half what the cord is designed to withstand and that the dissipation is now spread out over twice the length. Consider also that the 55 Amp rating for this wire is at 60 °C and OP is presumably at less than 0 °C. Thus there is clearly no risk to daisy chaining two, three or even four of these except perhaps to your wallet and back. They contain three pieces of #6 and presumably 1 of #8 and are, therefore, both expensive and heavy. You would, with 4 in series, lose 6.27 volts and thus, at 32 amp draw, obtain only 7479 Watts compared to 7630 with 1 (assuming 240 V at the outlet in both cases). There is certainly no need to reduce the charging current.
The NEC does require going to larger gauge if the run exceeds a certain length. That is done to insure that the voltage at receptacles is not degraded. But we are not wiring a building here. The code does not apply here, the car can clearly deal with the reduced voltage (down to 110) and we are not running in conduit, behind walls etc.
