I've noticed that I suddenly have a lot of AA battery powered photo gear. There's the A95 which serves as my light/flash meter and photographic sketchpad that takes 4 AA batteries. There's 2 Sunpak 383 Supers and a 1 Sunpak 144PC, and each one takes 4 AA batteries. There's the kinda cruddy Sunpak Digital Flash that is now just used to trigger slaves off of my RB67 that takes 2 AA batteries. Finally, there's the Quantaray QS-1 that takes 2 AAA batteries
Meanwhile, the Mamiya RB67 takes no batteries at all, and the Canon TX takes a single button cell that lasts forever. But I think Nicolai covers how I can't go on about how cool this is quite well. :)
If you count up, there's clearly a need for fully charged 18 AA batteries at any time.
The first battery charger was a dead simple trickle charger. If I took it apart, I'm sure I would find two channels of current limiters. Batteries are charged in pairs, overnight. I slowly started acquiring rechargeable AA batteries so that I could have a set for the A95 and the 144PC (which was the only battery-sucking gear at the time) and be able to swap out batteries.
When I went to Peru, I picked up a universal-voltage charger. It was also a fast charger. This is when I started noticing battery hell. The symptoms are that I'd charge a battery but it would appear to be dead when I put it in the A95 instantly. I started carrying alkaline batteries as backups because I couldn't trust that I'd have sufficient numbers of rechargeables. I figured that I just had grabbed the wrong set the first few times it happened. I'm sure if I took that one apart, I'd find some amount of circuitry that doesn't quite detect when a battery is fully charged and very likely it also charges in pairs.
I found out that there's a lot of weird myths and half-truths about rechargeables. For example, most times when a battery starts acting up, it's not actually the "memory effect". Often times, it's that you need to discharge the battery all the way and the battery puts out low voltage that convinces the camera that the battery is about to die... but there's still plenty of power. Or the cells in a set have worn differently so one battery never quite gets enough charge or discharge. Things like that. The fun part is that if the cells in a set get too far from each other, you'll ruin one battery out of the set.
The BC-900 is nice because each battery has it's own channel, so you can ensure that each battery gets topped off at the proper rate. All of my battery sets had some degree of imbalance between the individual batteries in the set, such that sometimes a battery would take an hour longer than the others to go through the charge/discharge cycle. This was most evident in the set that I caught acting like it was dead right after a charge. Now it works fine.
It can also discharge a battery all the way down before it charges it, which will make the batteries behave better. Plus, there's a "refresh" mode for batteries that have low voltage problems that discharges and recharges them repeatedly. It even lets me specify how much of a rush I'm in, letting me charge it at a slow battery-life-preservation rate or charge it quickly if I need a fresh battery fast.
I can tell that the LaCrosse has been designed properly even without taking it apart. The only real flaw is that the button interface is a smidge clunky.
It got worse before it got better. I was in uber-battery-hell, where I had NO idea if the digital camera would work in a given situation, so I just stopped shooting the digital P&S camera at all unless I absolutely needed it. I ended up using the "Refresh" mode on the LaCrosse on a few sets and throwing one set out. I also got a few extra sets of batteries, so that I'd be certain to have backup batteries.
I shot three rolls of IR820c so far. I've got the third one hanging in the shower right now. I'll talk more about IR film availability and stuff later this week.