An electronic flash strobe, powered by AA batteries, will slow down sooner than you or I expect. Recycle time, the time from one flash to the next, will become longer as power is drained from the batteries. (And if you use rechargeable batteries, those usually do not hold out quite as long as standard alkaline batteries.) How can we prolong optimum power for a flash? The short answer is: a better power source.
If you’re using a flash that’s built-in to your camera, then you are probably stuck. The only thing you can do is carry an extra supply of charged batteries and change the battery more frequently. The good news is you may be able to use a more powerful external flash, even though your camera already has a built-in flash. But to answer that for your particular camera, you have to check the owner’s manual.
If you’re using an external flash, powered by standard AA batteries, many flash strobes will allow you to use an alternate power source, instead of the the battery compartment built in to the strobe. There are a variety of possibilities and some can have a price tag much greater than the strobe.
Typically, I am using a Canon 580EX2 strobe, which has a power socket allowing for an external power source. Canon sells an external battery pack CP-E4, which holds 8 AA batteries, twice as many as the built-in battery compartment of the 580EX2. However, with a retail price tag around $150, the CP-E4 seems over-priced. Seriously, it is a simple battery holder, no fancy electronics involved.
Thankfully, there are less-expensive 3rd-party equivalents. If you use one of these, it likely invalidates your Canon warranty and Canon will not guarantee that their products will function with a non-Canon battery pack. The 580EX2 instruction manual states: “If non-Canon, external power pack is used, it may cause malfunction.” Does that scare you? It shouldn’t. Canon is simply protecting themselves from liability if you happen to connect a defective power supply.
I’ve been using a Bolt CBP-C1 battery pack; like the Canon battery pack, the Bolt holds 8 AA batteries, but the price tag is half that of the Canon. It has proved to be durable and reliable for photographing sports, weddings, and stage performances. I have been using rechargable Sanyo Eneloop batteries (NiMH). Using just one set of batteries, I have not yet run out of power during any shoot.
One little trick to be aware of regarding the use of an external battery pack with the Canon 580EX2 strobe. When an external battery pack is connected, the strobe may rely in-part upon the external batteries and in-part upon batteries installed directly in the flash. If you have particularly weak batteries installed directly in the flash, the flash may fail when those batteries fail. You can change this. Among the cryptic custom function settings, you will find custom function 12. Set custom function 12 equal to 1 (on) and the flash will exclusively use the external battery pack.