Congratulations on your first scooter! Excellent choice! (also a lot of scooter!)
Go with the volt meter. Check the user manual and P-settings to find out the cut-off voltage for your scooter. (I’d check ours but I’m not in the office today).
If it helps, our Vsett 10+ covered 33.6 miles (54km) in dual motor mode, top performance settings, averaging 18.6 mph including starts and stops (typically running up to about 28 mph between stop signs).
Keep in mind the batteries have less energy per volt at the beginning and ending of the voltage range. So the voltage will change more quickly at the beginning and ending.
-Paul from ESG