Aplus Case 2 Packs of Universal Zipper Zip Travel Carrying Waterproof EVA Storage Bag for 4 x 18650 Batteries (Also Fits Cellphone Charger, Cable, Earphone, USB Flash Drive)

Works perfectly for 18650 and 20700. You can shove 4 21700 but its a stretch and they are hard to remove. If you want to use them for 2 of any of the batteries I mention and some other stuff like coils, cotton, small tools, ect. these are amazing. They are thicker than other battery holders but not much and the extra they can carry makes up for it. The quality of the 2 i got is great and it looks like they will hold up well I will update if not

These are just perfect! I had these cheap plastic cases that would just pop open and my vape batteries were flying around in the chasm that is my purse, which is, of course, horrible for the batteries, and a potential safety hazard. I tend to take a lot of road trips so I keep at least four sets of batteries. These make it so they’re nice and secure in the cases, the wraps aren’t getting damaged or gunked up, and I can easily tell which ones are dead or alive by my habit of putting good batteries plus side up. They also hold a couple flash drives and a chap stick, or spare coils, whatever you need to fit in there, with no issue. I can see many uses for these little cases. But if you need a good case for your 18650s, this is exactly what you need!(And just for the sake of the times, fitting a mask in one side is do-able. A folded neck gaiter is just a touch too large, but a standard mask will fit just fine. I don’t have one to use as an example in a photo, but it can definitely be done.)

You get exactly what you're looking for! The zipper seams durable, the material is thick and sturdy. Elastic is nice overall these are a great value for the money. 10/10 recommend.