As many others have complained the stock battery carrier on the BTU is very simple but robust. The batteries have to be carefully placed in the carrier so they make full contact. I can also see the light losing contact with the terminals if the light is bumped hard.
Here is an example of what I mean (picture from Shaquille):
When I noticed this problem I thought to myself, "This should be an easy fix!" Sure enough it only took about 15 minutes. Mostly because I am OCD and they all had to be exactly 8mm. I used electrical tape but any kind of tape would work. The carrier now works great and the cells fit perfectly with no chance of them moving around.
Here are some pictures:
If you own a BTU do this simple mod, it is definitely worth the time. 
What kind of wrap around material you’re using on the rod? Is it necessary to detach rod from battery holder?
Electrical Tape.
It helps a lot to remove at least two of the rods.
Thanks for the tip.
Thanks for the tips…. it works 100%.
You get a award from TBU factory in Hongkong
I just got my Shocker, and I couldn’t “get” this mod, until I had the light in my hand. I think I’ll try it now :)…
ill have to try this