Please note: If you are not proficient with soldering, working with electricity, and Li-Ion batteries*, do not attempt this mod. I, Ultrasabers, this community, and the Force are not responsible if you destroy your saber, hurt yourself or others, burn down your house, or, well, anything else horrible! The only thing I'll be responsible for is if you successfully mod your saber in the manner described herein based on these instructions.
Performing this modification WILL void any warranty your saber has with US.
There are numerous soldering tutorials on YouTube and the Interwebs. You should also be sure to heat shrink all your connections, because again, a shorting out Li-Ion pack is a very dangerous thing. Electrical tape is NOT sufficient, it WILL fall apart after a certain amount of time.
Good luck, and may the Force be with you.
(*Lithium Ion batteries, moreso than other types of rechargeable batteries, are
EXTREMELY DANGEROUS if mishandled. These batteries will rapidly overheat and may even
EXPLODE if shorted out. Always remove the batteries from the battery pack while performing work!)
I believe I labeled everything important, and even unimportant, if I'm correct. QD stands for Quick Disconnect, which you'll probably need just to get your saber back together once this mod is done.