I was wondering what this 'line' is. I suspect it is some form of indication of the battery voltage, and i think maybe the little mark in the middle is some 'low voltage treshold' indication. Hope someone know for sure as the manual is really not any helpful (Especially for someone with no previous experience with R/C computer radio).

The maximum battery voltage should reach at least 11.0v after charging for 14 hours (atleast all my radios with an 9.6v battery pack have 11.3v when I unplugg the charger).

If I'm not totaly mistaking, I think the manual says that you can use the radio for about 5-6 hours on a full charge. But I personally would not use the radio if the voltage gets too far below 10.0v