There are 3 lights on the motor control box. When all 3 lights are lit, the battery is fully charged, at 2 lights it is 2/3rds full, and at 1 light it is 1/3 full. The unit will shut off by itself before it would allow the battery to drain to a level that would damage the battery. There is also a setting in the app that shows the voltage for the battery.
IMPORTANT NOTE: If you are using the battery to power or charge an accessory used with the MōVI, it is your responsibility to constantly monitor the battery’s voltage through the use of a voltage checker. If the accessory drains the battery below 3.0V per cell, it will damage the battery and render the battery unusable. Never attempt to charge a battery that has individual cell voltages below 3.0V.