As far as battery technologies go I really don't understand the reason for using a LiPo in a low current demanding situation such as the transmitter. Far more suitable technologies are NiMh, NiCad, LiFe, Lion, as these are less likely to suffer damage if discharged below the theoretical 3.3Volt per cell. Only the other day I left my Taranis switched on in the boot (trunk) of my car by accident and completely discharged the 2000mAh Ni-Mh battery pack, it just meant I needed a much longer charge than
normal. If this had been a LiPo battery it would have needed some special treatment to bring back to life, and even then wouldn't have guaranteed a successful resurrection.
As for the Phantom transmitter, which only has a current draw of a few hundred milli-amps at most, AA cells are more than adequate. A set of reasonable 2900mAh Ni-Mh AA batteries are very cheap and last an age and don't have the inherent risks of LiPo's when taken out of their comfort zones.
Regards
Nidge