If your battery has just been charged, 48.5V is far too low, as it should be somewhere around 54.5V.
If the battery is 6 Volts too low to start with, I'm not surprised it's shutting down under load.
I suspect that the
BMS is cutting out correctly due to the low battery voltage activating the
LVC as soon as the battery is subjected to any loading.
Either the correct charging voltage is not getting to the battery
(charger voltage too low or BMS not passing the current) or there could be a problem with some of the individual cells within the battery.
Try checking the battery voltage while it's on charge and let us know what the voltage reading is.
It would also help if you can check the voltage coming directly from the charger output plug, but be very careful not to short the meter probes together.
I would expect the charger output to be at least 54V.
Also I cant seem to figure out how to read the amps, all I get on the meter is 000.
Your particular meter is only suitable for measuring very low current
(0.2Amp max), if you were to try and measure your motor current with it, it would simply blow the built in fuse, so there's not much point in trying.
Alan