Excerpts from Steve at http://www.hangtimes.com/ (battery supplier)
:

... high temps affect any battery system. When the pack is hot, impedance is impacted, voltage is depressed, ability to accept a charge reduced, useable capacity is reduced, etc. Also worthy of consideration, vibration can pop welds, break down internal insulators and lead to catastrophic failure. Quickly.
.....That is NOT a suitable location for an Rx/Servo pack... period. Ignition pack, maybe.. with some precautions as indicated above. But the Rx pack up there.... never. Too close to the ignition field, too hot, too much vibration. As an Ignition pack.. ignition failure; you are a glider. Rx pack failure.. you are a pile of sticks. Rule of thumb.. don't mount a battery pack where you would not mount a receiver.....

Yes, I see that he warns against the R/F problems associated with a gas engine, but would not characterize the thrust of his concerns as R/F. It is one of three, with vibration and heat being the other. Why would you not want to eliminate these threats to the safety of those around you, not to mention the security of your aircraft?

littlera