I don't know if TCH would have a problem with reverse polarity and I'm not willing to check, but I know some Prius owners had issues. I think inverter , the one that charges 12V battery from traction battery uses Mosfet transistors and those will get damage with reverse polarity. The amount of computers and electronics inside TCH is much larger than in any normal car and those are very sensitive to any abuse. Even if the system is protected from reverse polarity with diodes, who says protective diode can not fail? Fully discharged battery will recover some of the voltage after it's left alone, which may be just enough to start the car after a while, but with the car in off position I don't believe there is any charge coming from traction battery, there is a relay that physically disconnects it from the rest of the system and it needs 12 V battery to energize and let recharging begin.