The batteries have a power management system which cuts off the power in order to protect the lithium cells. It sound like the cut off is working a little differently on your different batteries. The Voltage starts about 54 volts and once it has fallen to around 45 volts you are really out of juice.
Can’t really understand the trip meter discrepancy and range is dependent on a number of variables. I tend to think of it in terms of time- you should get around 1.5 hours of power so after about 45 minutes riding I start to think of where I am in relation to an accessible power socket.
Anyway great to hear you’re loving the bike!!!