There are many things with respect to the install that will effect the performance of the Datalink system.
I personally believe that the Datalink isn't really suitable for the Phantom as there is very little real estate to mount the device away from the other electronics and the main 2.4GHz control system but there are things you can do to make the most of the system.
It's very important that you have the antennas on the air end so configured as they maintain communication for different orientations of the craft. The system uses two sleeved dipole antennas on the air end. Ideally these should be positioned 90 degrees to each other. I have mine mounted on the underside of my Hexacopter with one antenna routed horizontally along one arm and the other pointing straight down. They are also located on the opposite side of the frame to the antennas for the regular 2.4GHz receiver.
The Ground Unit.
It makes no difference if you are using a 100mAh battery or a 10,000mAh battery, 3s or 4s, it will not effect the output of the unit. The unit is designed to be run from 5Volt, USB, the battery voltage is stepped down internally.
One very efficient way of increasing the range is to simply raise the height of the ground unit. I have used a simple three section 3metre telescopic fibreglass pole, the bottom three sections of a cheap telescopic fishing pole. The ground unit along with the battery and BT module are mounted to the top of the pole. If using the PC version I use a 5metre USB cable that also supplies the power so negating the need for a battery.
It's also worth noting that the antenna supplied for the ground end is not a simple dipole but I believe is a colinear type, sometimes advertised as " hi-gain ". The radiation pattern is such that the energy is concentrated more toward the horizon with a much greater vertical null than a dipole.
With this arrangement on my Hexacopter I have range tested out to a distance of just over 800m at an altitude of 50m, any further and it would have been a one way trip for my hex on the battery in use at the time.
Regards
Nidge