Stepping up the voltage for DC power makes the overcurrent protection insanely expensive, there is no ‘zero point’ for DC like there is for AC so circuit breakers are tricky to manufacture. Maybe fuses would work, I’m not entirely sure.

You’d be better off replacing the charger cables, in my best estimation.

AFAIK you can’t charge a battery with AC current, you’d need an inverter onboard the vehicle to convert to DC.