Good project to keep track of the charged/discharged cells. We have about 80 of these Eneloop, Eneloop Hi- Cap, and similar batteries we use for cameras and flashes and test gear. We use chargers that do not even charge in pairs. And we have several devices that do not even use pairs (both 3 and 5 cells used). I do not think pairing seems to matter as we mix and match all day every day and have not had any problems at all with them under pretty rigorous use. We use both Sanyo Eneloop chargers and PowerEx chargers.
This was a great use of 15 minutes. I agree with drbyte about the pair charging. Electric car guys claim that one battery can go bad (those are usually lead acid) in a group. Not sure about the types of batteries we use in all of our devices, but my charger identifies the ones that will not take a charge so I discard those (recycle). Various online posts give conflicting advice but I have not encountered a problem doing it this way.
dr byte I think we might be in the same line of work, but yes I have never cycled my batteries as pairs. Most chargers don't even work that way anyways as often as not they are sequential meaning they go left battery to right or the like. And many devices use odd numbers of batteries. What will make a difference, and is probably the whole root of the sequential charging thing has more to do with the date they were put in service. As the more cycles go on a battery the less effective life it has ahead of it. The simple way to track this is to date them when you put them into service… and that is really only important if you are using them for job critical things. Ie something where you might get fired or lose a client if they go bad quicker then they should in my case that is most frequently the radio microphones, for national level clients and the like…
Either way i might have to make one of these perhaps with a top piece or some kind of lid arrangement.
I tend to put them in use by pairs or fours… but that's because I've got a bit of the OCD bug and prefer to have them match! It also helps with consistency, though I know there's a bit more flexibility with the newer batteries than in the past. The eneloops are great - I use them with my photo equipment and they perform wonderfully.