Ah...

It could be the UBEC on the ESC is bad or one of the caps on it is blown.

If the pack fixed the problem with the tail servo as well ( a good sign! )... then I'd ask Eric or Andy for a replacement ESC.

The ESC/UBEC on my plane has no problems powering the servos... I believe I found the specs for the ESC a few weeks ago ( don't ask me where as I don't remember at the moment ) and I saw that it had a 2-3A capacity @ 4S and 2A @ 5S which should be more than enough.

At worst fly with another ESC and use the replacement ESC for another smaller plane.