GBA & DMG | How will I know when the battery is low?
The Game Boy Advance CleanJuice will turn the built-in low power indicator LED red when the battery is low, indicating 15-20 minutes play time left.
Note: versions sold prior to August 2020 require the Low Voltage add-on board to do this).
For the Game Boy Original the CleanJuice will turn the built in GB LED to a dimmer red when you have about 5% battery left.
Note: versions sold prior to October 2020 do not do this.