Since the charger's light turns red and then changes to green after a few seconds that is a good sign that the charger and charger port are both working, however if the charger's light is turning green when the battery pack is at 52 Volts (13 Volts per battery) then the charger may not be working properly as we would expect the charger to not display a green light until the battery pack Voltage was between 54 and 55.2 Volts (13.5 and 13.8 Volts per battery).
These Voltages (13 and 13.5/13.8) are so close to each other though that the problem could also be with your multimeter not being very accurate or having a low battery which can cause it to display incorrect Voltages.
I have a go bowen scooter 48v 1000w brushed motor, when I go to plug in the charger to the scooter the light would turn red and then after a few seconds it would go back to green. I checked all four batteries and they have 13 v so far. Do you know why the light won't stay red?