Correct me if I am wrong but why would you need to do that unless you are a battery pack designer?

First of all, this is only valid if you have the exact rated voltage of the battery pack, and that is an easy information.

And then, why would you need the capacity in Ah? You have you power consumption in kWh/km (or m/kWh) because you have to counter mostly forces that are already in W. Working in Ah is slightly more accurate when you know you consumption in A but that’s not the case. In the end for a driver it is much easier to work fully in energy domain and understand there are variations in the actual capacity (and max power) due to the temperature.