Just picked up a slg UL over the weekend and noticed the battery that was in the gun was dead so I changed from the stock proto to a duracell procell. After changing the battery the gun would not always turn on, and when it did the led would always fade and then the board would shut off.
Turns out the proto batteries are a little longer than the standard duracell or energizer 9v, the cure to this problem is to put a piece of paper on the bottom of your 9v to push it forward once installed. This will make a more solid connection between the battery prongs on the board and the battery terminals.
YOUR BOARDS ARE NOT FRIED! You're now saved