Most rear-wheel drive scooters utilize an electronic or electro-mechanical dynamic, regenerative braking system.  This type of braking system works in tandem with the motor, first to slow and then to stop the vehicle when the pressure is released on the thumb levers or the controls are otherwise disengaged.  When the scooter is not being powered forward or in reverse, the brakes are engaged, thus preventing the scooter from moving.  During the application of the brakes, excess power from the motor is channeled to the batteries, providing recharging.  Because the brakes are engaged when the scooter is not being actively powered, most scooters with this braking system are equipped with a clutch on the motor or another release lever to manually disengage the brakes to allow the scooter to be pushed in case of emergency.

Some scooters also use disc brakes alone or disc brakes in combination with the braking system discussed above.  Some scooters—usually front-wheel drive models—are not equipped with electronic or electro-mechanical brakes.  In the absence of a brake system, a manual parking brake applied by lever to a rear wheel is provided.  Manual parking brakes may also be offered either as optional or standard features on other scooters to provide extra braking on hills and inclines.

Source: ABLEDATA Fact Sheet on Scooters