Fully charged it should read 42.0 ( hot off the charger ) and left sitting overnight would likely be 41.x ... a short ride would have it resting at 40v but what you want to know is the voltage while it is plugged into the controller under load (accelerating, or going up hill ) .. gets trickly but tape the volt meter to the bike and test it out.. report back..

The BMS should cut out at 30v or so but that would be absolutely empty. not much left below 33v

When it quits, does the battery or controller feel hot/warm ?