I have an old HiTec Flash5X (72MHz)) transmitter that currently uses a 1000mAH 8cell nickel metal hydride pack. it works OK, but if I want it to last for more than a few flights I have to charge it the morning of or at least the night before or it will lose it's charge sitting. I know a 3 cell LiFe pack is close to the same voltage and lithium batteries can hold a charge for a very long time (lithium-iron can better tolerate full charge storage also). They also last a lot longer and I have even seen them made in an 8 AA battery size for transmitter use.
HOWEVER, I am concerned by the voltage differences and discharge curve. Also the low voltage warning in my older TX which is calibrated for 8 NiCd or NiMH. Can I use a LiFe pack in my transmitter without harming it or the battery pack?