When I power my Arduino uno with a 9v I thought that the second ground pin (the one the battery is not attached to) could also serve as a ground source for an lcd display but it does not. Is this correct? I think that I cannot use the direct 9v ground for the battery as the same ground for a 5v lcd. how do I arrange this?
Perhaps you have a bad quality clone Uno board, but every GND pin is the same and you can use every GND pin for battery or lcd or anything else. You can use seperate GND pins or connect them to the same GND pin.
The Arduino Uno has three normal GND pins. The ground of the power jack is also connected to GND, and the ICSP header has a GND pin. They are all the same.