A simple 18650 single-cell battery case with or without knurling and a hanging hole at the bottom.
Do you want to carry batteries with you, but don't want to just throw them into your backpack? Are you worried about them getting mechanically damaged or getting wet? Now you just need to print a battery case like this, and you can rest easy. It's easy to open and close, sturdy, and well-designed. The inner diameter is 18.9 mm, and it will shrink after printing, making it easy to remove your batteries