To ensure range preservation while riding on low battery, the scooter will automatically reduce its speed from the performance speed setting (Red "D") when riding on low charge.
As lithium batteries discharge while riding, the nominal voltage output of the battery will slowly decrease as well. This means when you are riding on low battery, you won't be able to reach the maximum speed and acceleration as with a battery that is fully charged.
When the battery is below a 25% charge level, the speed mode will automatically be reduced to Eco in order to preserve the range on the scooter. This is not a feature that can currently be turned off.