I use tired flight batterys ! I have two 9x and three 9xr radios.
One 9x has still the NiMh in it and works a charm with Smartieparts basic board. Flies my FlySky / WLtoys stuff. I use a Futaba M series charger from the 1980's ... Second 9x has a 3S 1500 LiFe pack in it and powers the brilliant AR9x board ... which sadly is no longer available. One 9xr has the Turnigy 9xr 3S 2200 low C rated Tx LiPo which has been excellent - but can only be charged at max 1C The other two 9xr have old common 2200 / 2400 3S LiPo's in that are now no longer good for flight motors - but are still more than capable for the low Tx power. I charge ALL of them outside the Tx cases by usual LiPo / LiFe chargers ... There actually is no real need for special Tx packs ... its in my view a marketing ploy. I even use old LiPo's via uBEC in gasoline and glow planes ... just because they cannot thump out 20A or so for a motor does not mean they cannot supply 5A or so for Rx / servo use. Average Tx demands about 300 - 600mA ..... its why NiMh are fine in Tx's ...
I'll fly anything if I can launch it ! Youtube : solentlifeuk