The best way to truly assess reduced range is to ride the battery from a full charge until it's completely flat.
Please do the following:
Use a ride tracking app, such as Strava or MapMyRide
Starting with a fully charged battery, take a picture of your display, showing the main odometer and battery status.
Ride until the battery is completely flat.
Take another picture of the display, showing the main odometer and battery status.
Send us the pictures, as well as a link to your data from Strava or whichever app you used.
Once we have this information, we will be able to assess the condition of the battery.