I have gotten deep into bird photography this year, and have put a lot of time and effort into learning the tricks of the trade. My latest endeavors are into bird/bif flash photography. I own a Canon 430EX II flash, and a flash extender (basically a simple Fresnel lens on the end of a couple of arms that attaches to the flash head.) I've spent the last several days learning how to use my flash, primarily in manual mode, how to use the flash extender, and how to use the two along with my 7D to provide some fill flash for my bird photography. Lately that encompasses my back yard most of the time, which is full of a whole variety of black birds...which can be a real pain to expose for correctly a lot of the time.
I have noticed that my flash recharge/recycle time is HORRENDOUSLY SLOOOOOW. I have my camera set to low-speed continuous, as its more convenient for shooting birds on branches and around my feeders. Even with low-speed continuous, I usually only get a flash burst on the first shot and none for the rest of the sequence, and some of them can be as much as 10 frames (or more...I can get over 30 shots continuous if I just hold the button down, and I still only get flash on the first frame). I switch to single-shot mode now when using the flash, however I can only really get about one shot off every 15-30 seconds. I figure the root of the problem is the simple alkaline AA batteries I'm using, which I know are not known for their speed. I figure I'll need to invest in a bunch of good rechargeable batteries to solve the problem.
Getting specific, what type of rechargeable batteries would be best for this kind of flash photography? I would like to use flash with short bursts (3-5 shots usually, multiple sets, often separated only by as much as a few seconds), and it would be ideal to get flash on all shots in a burst. If I have to wait a little bit longer between bursts that would probably be ok. I am sure there are well-known rechargeable batteries/brands/types for use with flash photography, perhaps even more advanced devices that can reduce recharge time further (maybe some kind of multi-set battery pack that has several groups of four batteries which can be used in sequence for rapid flash shots?) I'm not sure I could get it down to less than a second, but as short as technologically possible would be ideal.