Badmotor said:
... ... Or could it also be that my battery is simply dying and can't provide enough current ? I've used it for about 3 years now.
A battery is as good as it weakest cell. The BMS must keep all cells on the same Voltage. If just one cell has a too low Voltage the BMS cut the power. After some time and degredation of the cells a BMS isn't fast enough anymore to keep all Voltages equal. There a two types of a BMS.
The cheapest type keeps the Voltages of the highest cells down by a resistor till other cells are the same too. This cost a lot of time and can only compensate just a small difference in Voltage and does only work when charging.
The other type is more active and compensate faster between the cells. The higher cells charges the lower ones too. Also with discharging. So the difference between cells keep small as possible in time.
If you had flashed v20.1b before and now the latest v20.1C.1, fieldweakening is enabled.
That works at the cost of more current with lower Voltage. That is why your motor shuts down faster.
An advice is to open the battery, measure the Voltage of each 10 cellblocks and charge the weakest one seperately or discharge the highest ones with a resistor till all cellblocks are equal.
After this you can use your battery some time depended how bad that weakest cell(s) is.
If there is some space in the batterycase you can add an
active balancer parrallel to the BMS, which keeps the Voltage between cells the active way. No guarantee this works for you, because the unknown state of the weakest cell(s).
Eventually replacing the weakest cells with the same celltype is also an option, but in that case I advice always to use an active BMS/balancer.