I made some duct tape cases for my batteries without plastic covers. But I wanted something better. I happened to lay eyes on my soft Bubm 6 USB Flash Drive neoprene pouch (can’t find that one on Amazon, but saw it on a UK website), and found that the elastic fits the batteries. I used a 3d liner to mark them, because that makes it easier to go through them sequentially.
BTW, there’s no category that really fits my hack posts…