After working on a few projects, we come up with our own solutions that help us to be more efficient. For organizing batteries, I know many (including me) use bags to store and separate charged up vs non-charged batteries. It works, nothing complicated, and inexpensive. But if you're looking into being a little more organized while helping out a fellow filmmaker, check out the Battery Mag.
The Battery Mag is a simple camera battery organizer that allows you to keep your Canon / Panasonic / Sony / Nikon / Fuji camera batteries organized and tidy in your camera bag. Know in an instant which batteries are charged and which are dead. Designed by a Documentary cinematographer to make life in the field a little tidier and a little easier.
Here's what I like about the Battery Mag. The case prevents loose batteries from shifting around in a bag and protects the contacts (terminals). It also shows you how many batteries you have missing. Often when i'm working with other people, we share batteries. So it's an easy visual to account for any missing batteries that haven't been placed back in to your bag. So yes I know we can all save money just using simple bags to store batteries, but in case you find the Battery Mag a good solution for you, more information is at Tim's website at http://Batterymag.co. (thanks Tim)