I just tried this as I was almost sure that there was no way that the end cap that US provides would fit on the bottom of a x4 AAA battery pack. It does because it is so flexible. I still needed to use some Velcro to entirely stop the pack rattling which I placed above the black cap. Now fits securely and still slides out without any significant hesitation.
point
Worked well for me, I was surprised that it fit myself i had been just putting it in side the hilt so the battery pack would stop shifting up and down, I went to change battery's and the pack had worked its way into the rubber cap so I just put it back on afterwards. Happy accident!
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