Montana 7xx Blue Battery Status Indicator

The Montana 700i and 750i periodically will change the green battery status indicator from green, to a blue battery with an exclamation point. It is intermittent and sometimes will go back to green again. 

Both devices that this have been observed on have been on external power using the Garmin AMPS mount using 12v power. When the device is removed from the cradle, the battery status indicator will return to green.

Does anyone know what the blue battery icon indicates?