[Blackthorne]

I'm no expert on AEG's, but this is my diagnosis based on your symptoms.

It fires well and long on Semi, but seems to drain the battery after 4 when on Full Auto.

I figure one of two things are possible:

1: When you switch it to Full Auto the movement of the fire selector switch is shorting/grounding the battery (via pinched wire or something) on the mechbox' metal and discharging the battery almost instantly.

2: When you switch to Full Auto the movement of the fire selector switch puts pressure on the internals and wears the battery down quickly.

2 seems unlikely unless you are noticing a drop in FPS/distance. Friction will make a noticable difference in this area.

My bet is one. Something is draining the battery when you throw it into Auto