LM311P op-amp strange behavior in comparator mode
12V relays to turn off a scooter from low voltage will create many new problems.

Most automotive power relays activate slowly “must switch” at 50% of rated voltage so 7V for a 12V relay rated for 14V nominal and Must switch off at 10% or 1.2V voltage but “may” switch off sooner. 

All great relays have at least 50% hysteresis. Yours must have a weak spring.

The new problem is that batteries also have memory or hysteresis voltage effects with step load currents and this will force you to define acceptance criteria depending on current due to the ESR in batteries.

Motors also arc contacts badly until the motor stops or is switched off electronically forcing you to get a big snubber to absorb the motor/generator energy.

At the end of the day , you will be better off having a loud alarm buzzer that alerts the driver to stop.    You could also sense high current and low voltage and logically AND them you can get by with a power calculated threshold to enable the alarm or some other soft limiting feature for power with the throttle control. 

The alarm threshold might be like reserve fuel level , leaving enough time to drive to a charge port.