Perfectly snug fit for my USB battery pack. Not sure what others it will hold, but it holds this Lekzai one like a glove: https://amzn.to/3nZFsgh (affiliate link)
Let me know in the comments if there are other very common battery pack sizes and I'll add some versions.
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For the full video of my HSW wall check it out on the Fix This Build That YouTube channel: https://youtu.be/NsBqs3TRjqQ