I still think what you’re noticing is by design. What scooter is it?
Range/power is not linear. So going from 54.6V (100%) down to 48.5V (60%) and 18.3miles, does not mean you’ll get another 18.3miles going down to 42V (20%).
When you draw 1200W peak, and your battery is full, that’s 1200W/54.6V = 22A draw from the battery.
When you’re at 48.5V, pulling that same 1200W means you’ll be drawing 1200W/48.5V = 25A from the battery.
At 43V, trying to pull 1200W means you’ll be drawing 1200W/43 = 28A from the battery.
So you can see that the lower the voltage, the faster your battery will drain if pulling the same watts. That’s why scooters limit output as the battery gets more depleted. Let’s say that your scooter has a 25A draw limit on the BMS and anything above that will cause it to throttle. So when you’re at 43V, you can travel slow, but as you push the throttle too much, the draw is too much and your BMS shuts down the output and your motor sounds like it’s dying.
There’s also the issue of voltage droop. The heavier the throttle, the more amps and drawn and the more the voltage droops. So at 43V, if you try and go full throttle, then the voltage might actually droop to 42 or 41V, at which point your BMS thinks the battery is dead.
Hope that makes sense.