I have been using these Batuca battery cases for about 2 years now and they are the best that I have used. They can be used to hold and organize AA and CR123 sized batteries. It splits into two sections and each section is a contrasting color. There are several different colors available. The lid snaps shut securely and opens easily by lifting a small locking tab. They are even made in the USA.
The split sections allow you to tailor the amount of batteries that you need to carry. They can also help you organize your batteries. If you use rechargeable batteries you can keep fresh on one side and spent ones on the other side. There is a ton of organization potential.
These make a great addition to your hiking/camping gear or your EDC gear.