ORIGINAL: SN VipeR
But if you have a good charger, want to save weight, have better runtimes, don't want to cut open your RC box, check out the link I wrote on my above post. If not, don't.
I would think long and hard about using LiPo batteries for an Tx pack.
For one thing, you have to have the right charger, one specifically designed to handle LiPo batteries... otherwise, they can catch fire/explode. It is also advised to observe the batteries while charging so as to be able to react in the event of a problem.
Second, LiPo cells are rated at 3.7v per cell, with two cells being rated at 7.4v. Typical servos are rated for 4.8-6.0 volts. That means one cell isn't enough, and I really don't know if the servos can handle the extra voltage of two cells. They might, but it could also burn them out or severely shorten their life.
Third, a crash or a hard knock can rupture the battery, potentially causing a fire or explosion. The recommended wait in the event of a crash is 1/4 to 1 hour, depending on who you talk to. On a related note, shorting the battery can also cause it to catch fire.
Finally, there are a number of other side issues to be concerned about, such as disposal of the battery, not exceeding the minimum voltage, etc.
Considering the expense and potential hazards involved, I have serious doubts that converting to LiPos for your receiver is worth the trouble.