Most likely the requirement is for Wh (Whatrs Hour), it is confusing but different from whatt.
The first measure the maximum nominal amount of energy that can be store in the battery the second is a power measure (like horsepower).
But your line of thinking is logical:
Power (whatt) = diferencial of potential energy (volts) x current (ampère).
So yes, as you drain the battery the ‘voltage’ drops and in consequence the power with it.
But to actually calculate the voltage in a certain SOC (state do charge) is not easy. You need a lot of info on the pack. It’s easier to measure it.
Going full circle back to the topic, most likely you will not be able to check your scooter.