Given the fact that at least once a season I either leave the transmitter or a receiver pack on I'll stick to my NiCads! Do it with a Lipo pack and you'll be replacing it. I usually only fly for 4 hours or so at a time so the longer life the Lipo pack offers doesn't matter to me. The ability to put the pack on a C/10 charge for 16 hours and have it perform like new is worth the extra weight. I'm only a sport flyer so I don't care about shaving a few ounces off the airplane. Your mileage may differ.
John
PS Gulliver
According to Don Schulman, all transmitters have a voltage regulator that will handle 15v.
Given todays cost cutting programs I certainly wouldn't take that advice to the bank. I'm not saying your 9C doesn't have a built in regulator but I certainly wouldn't give it a blanket statement like that.