Melex N Car Help

[day]

I installed all new batteries in my late model Melex N Car 343 cart. The cart ran as normal and then it was charged overnight. The next day it would barely creep along at 2-3 mph if that. Voltage has been checked and it is holding 50+ volts. Wiring has been checked. The batteries were disconnected overnight in order to reset the computer. None of this has helped. Any thoughts or advice would be very much appreciated.