in my 9303 manual i believe it said that fully charged 3s battery is to high of voltage and it can overheat the rf deck. i have even talked to some service guys there and they said the same thing. if the rf deck overheats you loose your range. charging a lipo to 11v is probably the best and safest route to go.Horizon will tell you NO! The Horizon guys will tell you the JR and Spekrum Radios are not able to take anything above the rated voltage of a fully charged NiMH or NiCad pack, period. Since a fully charged 3S Lipo can be as high as 12.6V, you are well over the nominal 9.6V conventional 8-cell pack that can be charged to as much as 11.9V.
To me this is a line of BS, but they are not going to tell you it's okay. The manual does NOT specify the max battery voltage. However, the issue they are likely concerned about is that you may try to charge the LiPo in the Radio, where the Charger pushes voltages way over 13 volts. If you're gonna go LiPo, don't charge in the radio!