It's imo usually easier to calculate Watts rather than Volt or Ampere when trying to figure out how different pack sizes will affect performance.
When the controller switch down the voltage (say from 150 Volt pack voltage to 50 Volt motor voltage) it's at the same time switching down the current the other way (say from 600 Ampere motor current to 200 Ampere pack current). I'm happily ignoring the switching losses here since that would just make things a lot more confusing...
45 100 Ah-cells would mean about 148.5 Volt (using 3.3 Volt per cell as some kind of number out of a hat here) and 14.85 kWh.
50 90 Ah-cells would mean about 165 Volt and 14.85 kWh, ie from a range perspective this would be equivalent.
So how does this affect performance? Well, not much. Let's say your motor pulls 500 Ampere at 100 Volt,for the 100 Ah pack that'd mean that as voltage goes down from 148.5 to 100 Volt, the motor current of 500 Amps results in a battery current of about 337 or a C-factor of 337/100=3.37.
For the 90 Ah pack that'd mean a voltage from 165 to 100 volt and thus a resulting battery current of 303 Ampere, or a C-factor of 303/90=3.37...
So the two packs are (almost) equal performance wise despite different pack voltage and Ah!
The only difference of the packs is that the 90 Ah pack can provide a maximum motor voltage of 165 Volts where the 100 Ah pack will only reach 148.5 Volt (minus sag, of course) so the 90 Ah-pack will give the motor a higher top RPM. The torque curve at motor voltages below 148.5 Volts will be identical for the two packs.
That's why I've tried a few times to sell the idea of thinking of a motor controller as a power converter rather than a current control system. If you have, for example, a pack of 90 Ah and 165 Volt that can handle a C-factor of, say, 4 you have a 90*165*4 which equals about 60 kW (not to be confused with kWh...) pack. Those 60 kW can, on the motor side, be converted to 60 Volt and 1000 Ampere as well as 120 Volt and 500 Ampere (since both those numbers equals 60 kW).
So the different units will limit your performance as this:
- Max controller current (A): Peak torque
- Max pack voltage (V): Top RPM
- Max pack effect (kW): Max motor effect (ie horse powers)
- Pack energy (kWh): Range
Did that make sense...?