An electric vehicle assembly, comprising: an electric vehicle carrying a user thereon and including a wheel, and an electric motor configured to drive said wheel to rotate, and to output a value of torque force applied on said wheel and a speed measurement of said electric vehicle; and a processing device including an output unit, and a processing unit that stores a vehicle weight which is a weight of said electric vehicle, that is electrically connected to said electric motor and said output unit, and that is configured to implement a monitoring procedure including receiving a first value of torque force at a current time point from said electric motor, receiving from said electric motor two first speed measurements of said electric vehicle respectively measured at the current time point and a previous time point, the previous time point being a predetermined time interval earlier than the start-up time point, obtaining a first acceleration based on the first speed measurements and the predetermined time interval, obtaining a current user weight based on the first value of torque force thus received, the first acceleration and the vehicle weight, and characterized in that the processing device implements the monitoring procedure that further includes controlling said output unit to output a first notification to remind the user to drink water when the current user weight is lower than an initial user weight by a first predetermined ratio of the initial user weight, and wherein the monitoring procedure further includes controlling said output unit to output a second notification to remind the user to drink water when the current user weight is lower than the initial user weight by a second predetermined ratio of the initial user weight, that is greater than the first predetermined ratio. an electric vehicle carrying a user thereon and including a wheel, and an electric motor configured to drive said wheel to rotate, and to output a value of torque force applied on said wheel and a speed measurement of said electric vehicle; and a processing device including an output unit, and a processing unit that stores a vehicle weight which is a weight of said electric vehicle, that is electrically connected to said electric motor and said output unit, and that is configured to implement a monitoring procedure including receiving a first value of torque force at a current time point from said electric motor, receiving from said electric motor two first speed measurements of said electric vehicle respectively measured at the current time point and a previous time point, the previous time point being a predetermined time interval earlier than the start-up time point, obtaining a first acceleration based on the first speed measurements and the predetermined time interval, obtaining a current user weight based on the first value of torque force thus received, the first acceleration and the vehicle weight, and characterized in that the processing device implements the monitoring procedure that further includes controlling said output unit to output a first notification to remind the user to drink water when the current user weight is lower than an initial user weight by a first predetermined ratio of the initial user weight, and wherein the monitoring procedure further includes controlling said output unit to output a second notification to remind the user to drink water when the current user weight is lower than the initial user weight by a second predetermined ratio of the initial user weight, that is greater than the first predetermined ratio. receiving a first value of torque force at a current time point from said electric motor, receiving from said electric motor two first speed measurements of said electric vehicle respectively measured at the current time point and a previous time point, the previous time point being a predetermined time interval earlier than the start-up time point, obtaining a first acceleration based on the first speed measurements and the predetermined time interval, obtaining a current user weight based on the first value of torque force thus received, the first acceleration and the vehicle weight, and characterized in that the processing device implements the monitoring procedure that further includes controlling said output unit to output a first notification to remind the user to drink water when the current user weight is lower than an initial user weight by a first predetermined ratio of the initial user weight, and wherein the monitoring procedure further includes controlling said output unit to output a second notification to remind the user to drink water when the current user weight is lower than the initial user weight by a second predetermined ratio of the initial user weight, that is greater than the first predetermined ratio.