Your motor CAN be damaged too as also your trigger switch.
And dude WTF? Duct tape under a heatshrink?
Why can't you just add a fuse in there for a safe warning?
When you solder wires, use shrink tubes or electrical tape.
Make sure that anything showing copper is covered.
Make sure wires are not cramped up.
If there is too much wires causing cramped up wires, than cut them.
If you cannot do all of this above, buy a crane stock set and save yourself the trouble, or gun doc.
Why send the battery back for something you damaged?
Why don't you just buy more batteries?
You'll end up needing at least more than 1 in the future for games.