Rechargeable Battery Blues
Using several speedlights means using many batteries - at least four times the number of strobes and most likely eight times as many batteries as you have speedlights if you have a couple of sets for each flash.
Personally I only use rechargeable batteries - nowadays of the NiMH-type, Nickel-Metal-Hydride - which mark the current optimum between capacity, price and other traits you want from batteries.
They have a high capacity, no memory (like the old NiCd cells had) and keep their charge fairly well, and can be "topped off " - boost charged right before use - with no loss of capacity in the long run. They are also more environmentally friendly than previous types due to a large number of recharge cycles and the lack of the poisonous cadmium and other nasty substances.
The available capacity per cell is increasing year by year, and while 1,800 and 2,000 mAh (milliampere hours) was the norm just a couple of years ago, today's AA-cells have capacities of 2,300, 2,600 and even 3,000 mAh.
I recently bought a ton of 2,600 mAh cells for my flashes and compact P&S cameras - 24 to be precise, which equals 6 sets - added to the 5-6 sets of mixed breed and capacity that I had already. That's a whole lot of batteries... nice indeed when you use many, but a pain when you are trying to decide which are charged and which are drained, which belong together with which in sets of four and how to get them all charged from one day's shoot to the next.
So I have had to devise different strategies to stay sane and keep my rechargeable batteries charged and under control.
My first trick is to mark them all in sets of four. Some are easy to identify because I have only one set. They always travel together, but others were identical in sets of eight and after my mega-purchase I had six identical sets. I dug out a bright, red and a black marker and started marking them four at the time: rings, lines, pluses, two rings. I could have used numbers of course, but as long as the marks were different and easily discernible that didn't matter. Now I can grab the used batteries in my bag and easily match them in sets.
Second trick is a simple rule: charged batteries are bunched - in plastic containers, using rubber bands, in small ziploc-bags or whatever. If they are charged, they sit nicely together four and four. Used batteries are loose, just tossed onto a small pouch, plastic bag or pocket in the camera bag. If I need fresh batteries, I just need to grab a bunch that is... well, bunched.
Third trick is to get several chargers. I think I have five right now. The two of them are large, slow-charging, large chargers, two are small slow-charging chargers - one for my domestic 220 volts and one for the US 110 volts. And one is a superfast charger that can go in the cigarette plug in the car or use a 110/220 volt transformer and go in a plug almost anywhere in the world.
So now I can charge many sets of batteries in a hurry. The fast charger is tough on the cells. It runs the high capacity ones from flat to full charge in slightly more than one hour, but then they are also sizzling hot, which is in general a no-no for rechargeable cells. But it gets me up and running in no time in almost any location.
The two larger ones charge intelligently - slow and with control. When the batteries are fully charged they trickle charge to keep the batteries at top performance and even pump that little extra into the cells. One has a decharger built-in, which was used for NiCd-cells, but hasn't got the same effect on NiMH-cells as far as I know.
Freshly charged batteries have a larger capacity than ones that have been fully charged and stored. The NiMH-cells may loose as much as 10% of their charge the first 24 hours of storage and up to 1% per day after that.
So topping the batteries off before using them can vastly increase the number of pops in them. I don't know how many pops I get from a set, but Nikon says that you have a minimum of 130 flashes on an SB-800. I don't know what capacity cells they are using for that calculation, but this does roughly compare with my own loose observations. You can add capacity and lower recharge times by using the supplied SD-800 Quick Recycle Battery Pack - basically a kludgy battery compartment lid with room for an extra cell. I personally don't use it because it would greatly disturb my sets-of-four paradigm.
Depending on their capacity I usually manage on one set of batteries per flash during a shoot, but when working outdoors or in larger rooms where more light might be required, I mostly work my way through a couple of sets per flash.
I have been thinking about using a battery pack, but never really got around to doing something serious about it. Nikon has its SD-8A battery pack, which will supply the flash from an additional six AA cells and increase both capacity and recharge frequency.
I also thought seriously about building my own pack, which would consist of eight or even twelve AA-cells or maybe some higher capacity cells and simply plugged into the current battery chamber using some custom made gizmo. But I never got around to doing anything seriously about that either, and for now I think I'll just stay with my many AA cells.