BEMF

BEMF = (Vbattery*duty_cycle) + R*I + L*di/dt

For I = 0
BEMF = (Vbattery*duty_cycle) + R*0 + L*0
BEMF = (Vbattery*duty_cycle)
In this case, BEMF equals to (Vbattery*duty_cycle), so no current flowing to/from the battery and no torque on the motor.

For I > 0
BEMF = (Vbattery*duty_cycle) + R*I + L*didt
BEMF < (Vbattery*duty_cycle)
In this case, BEMF is lower then (Vbattery*duty_cycle), so current flows from the battery to the motor and motor will do a torque depending on how much current flows.

For I < 0
BEMF = (Vbattery*duty_cycle) + R*(-I) + L*(- didt)
BEMF = (Vbattery*duty_cycle) - R*I - L*didt
BEMF > (Vbattery*duty_cycle)
In this case, BEMF is higher then (Vbattery*duty_cycle), so current flows from the motor to the battery and motor brakes/regen (with torque depending on how much current flows).