Diagnosis
This is almost always due to rider weight, terrain, and tire pressure. Low tire pressure is the biggest single factor for range loss.
How to Fix It
Check and inflate both tires to the maximum PSI listed on the tire sidewall (typically 45-50 PSI). Use a bicycle pump with a pressure gauge. Do this weekly.
If That Didn't Work
The battery may have degraded from frequent full discharges or being stored at a low charge. Try a full balance charge: leave it on the charger for 12 hours after the light turns green.
Heads Up
Riding in Sport mode, up hills, or in cold weather will drastically cut range. This is normal for all lithium-ion scooters.