I modified my Spektrum DX3.0 to use one of my old heli packs.
I used an Align lipo rated at, 3s 11.1v 1900mAh 13c.
The TX is lighter now as the lipo only weights 144g.
Since the TX should be able to handle 12v there should be no problem. Plus the built in voltage alarm and display will help me keep track of the lipos voltage.
Remember you don't want to let the voltage per cell drop below 3 volts or else you will damage your lipo.
I did have to modify the back cover of the TX so there was enough space for the lipo. It involved sanding down the inner tabs with a rotary tool.