it should be pretty simple and straight forward to replace the servo. You just unhook the ball link and if it is held in by a zip tie, cut that off and slide it out (if it's held in by screws take those out), unhook the electrical connection, and note the position and orientation of the wires, reverse the process and put the new one in. Unplug the motors noting their position and polarity, and then arm the heli and level the swash plate with the swash links that go from the servos to the swash plate.

Honestly it probably isn't draining too much battery life. On my CPP the whole thing draws somewhere around 4A, and the max load if all three servo's are bound is 0.71A, average though is more like 0.10A

hopefully that helps you out =)