Can I just take a pause for a second to say that I love MOLLE webbing? I don't understand why nothing non-military makes use of it's capability to securely attach extra accessories to a backpack. It seems like something that should be more widely used among general hiking and camping gear because there really are a lot of cool little add-on things you can use it for.Anyway, inside the pouch comes a plastic case which can hold up to 8 batteries of size AA, AAA or CR123. (Apparently if one were so inclined it could also hold 5 shotgun rounds, or even a cell phone or iPod. I actually did put my phone in there once while hiking). The plastic case itself is actually two parts which can be detached from each other. I think I heard it described that some folks use the two sides for "new" and "spent" to keep track, but I don't use that method. I keep it full and just hope I can figure out which ones are spent. I've only had to change a battery out once so far so it hasn't been an issue yet.
I keep 4 spare AAA batteries in one side for my Petzl headlamp and 4 CR123 batteries on the other side for my little Leatherman LED flashlight.
The nylon pouch seems well built, the plastic case is not bad either. It does feel like the two halves of the case come apart rather easily, but if they're in their proper place inside the nylon pouch that won't be any kind of an issue anyway.
Some additional info: There's also a small grommet hole at the bottom of the nylon pouch for water drainage. I'm not sure if the plastic cases are watertight but I'd imagine they'd hold up okay for a short amount of time .
The velcro (or "hook & loop" since I think "velcro" is a specific brand) closure seems to stick out a bit, but it's secure enough.
Also the plastic case fits very snugly inside the pouch. You have to push it out from the bottom side of the nylon pouch to get it out so I'd say it's pretty secure.
I think it ran me about 15$US and I'm comfortable enough with that considering it doesn't feel like something I'm going to have to replace anytime soon.