That is right. The fully charged battery should read 12.5 volts.
Then at engine idle, it may be a bit lower but the voltage should increase with RPMs to 14.5 volts.
Be sure the scooter is on the center stand and the rear wheel is off the ground when you rev the engine to about 3000 RPMs.
That is fast enough. The voltage should not go over 14.5 or it may damage electrical components.
scoot safely,