RE: lipo reciever battery
you can get a 2 cell lipo. you'll have to get a 5.5 volt regulator or you'll burn up the reciever. You'er not going to save much weight by doing this. It is on the other hand a good way to get higher capacity with about the same weight.
here are a couple
[link=http://www.horizonhobby.com/Search/Default.aspx?SearchTerm=voltage+regulator&OverallCatID=]couple regulators[/link]
this might be all you'll need
[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXFBL0&P=7]fma[/link]