There are a lot of questions to answer. What was the MA of the battery? How many flights on the battery? How new or old were the switch and servo extensions? Have you cycled the battery?
On another forum there was a thread on power needs for Gs planes with hi-end servos. This probability doesn't apply to you, but it was found that a 100cc plane at idle was drawing 2 to 2 1/2 amps at idle on the runway and after a hard 3-d flight the power piked at 19amps. We also showed the the standard servo plug caused a 1/2v drop each.
On our 2.4 receivers power is everything and must be watched very closely. A 4.8v battery must be recharged when it shows 4.8 because under load it will drop lower. Same goes for 6v.
Standard servos won't have the amp draw as the high end ones, but still old wires, old switches can cause a voltage drop before it even gets to the receiver.
This apply s to all the 2.4 radio systems. Dennis