This one's a no-brainer. If you haven't heard, alkaline batteries are EXPENSIVE. But there's an alternative. And a good one. No, make that a great one. Nickel Metal-Hydride, or NiMH batteries. They cost just a bit more than the old-fashioned alkaline batteries, but they last forever, and your flash will love them. Click here to read more.
There are several advantages to using NiMH batteries in your flashes. The first one being that they are cheaper. Did you know that you can recharge a NiMH battery up to 1000 times? Alkaline AA batteries can be found for less than $1 each if you buy them in large quantities, like here.
But good, "professional" rechargeable NiMH batteries cost a little more than $3 each when you buy them. But if you factor in that you can recharge that $3 battery 1000 times, that battery now costs less than 0.3 cents. That's not "three cents"--that's "point three cents" each. Sounds enticing, doesn't it? But let's say you're loaded, and you can afford to pay over 300 times more for your batteries. Are there any other advantages?
This next one alone would sell me on the batteries even if they cost MORE than alkalines. What if I promised you a faster recycle time between flashes? "Recycle time" being the time you spend waiting for the red light to illuminate on your flash indicating that the flash is ready to fire again. Yes, it is an electrical fact of life that these little batteries pack a punch when it comes to things like this, and this is one area where they really excel.
Are there any disadvantages? Sure. You do have to remember to recharge them. If you are one of those people that always forgets to recharge your camera battery (or cell phone or electric toothbrush), then this may not be for you. But if you can incorporate the recharging into your workflow, I think you will appreciate it. One other thing is that NiMH batteries are known to "self discharge" over time. So, if you charge up a set of batteries today and don't use them, then in a couple of months, the battery will be drained--again, even if you don't use the battery.
What to look for when buying rechargeable batteries. Look for specials, of course, and always look for batteries with at least 2700 mAH (mAH=milli amp hours). More is always better when evaluating mAH--there is no such thing as too high a mAH rating. This is true for ALL batteries (although for larger batteries it may be rated in amp hours instead of milli amp hours). If you are looking for a replacement battery for anything electronic, always look for the highest mAH rating to get the best performance. Why do you want a high mAH rating? That rating alone tells you how forcefully the battery can push out electricity. So, you will want to most power in reserve to be ready to recharge that flash of yours as fast as possible and that power is rated in mAH's.
Recharging. If you haven't already invested in a recharger for your batteries, you will need one. There are a lot to choose from. I like the MAHA professional charger, but realistically, any charger will do. I'd stay away from any rapid chargers. In fact, the slower you charge your batteries, the longer they will last and the more charges you will get out of them. One thing I like about the MAHA is they have two charging speeds--regular and slow. I try to use slow whenever possible, but occasionally I do use the regular speed.
Of course there is one more reason to use rechargeable batteries--they are better for the environment. I can't remember the last time I threw away a battery in my house. Alkaline batteries have all kinds of bad stuff in them that quite honestly we don't need in our landfills.
If you want to read another good article on rechargeable batteries, read this page from the Strobist blog.
http://strobist.blogspot.com/2007/09/feed.html
This is a good website to purchase batteries and chargers:
http://thomasdistributing.com/
I like these batteries:
http://thomasdistributing.com/maha_2700_rechargeable_batteries.php
But these look very promising too:
http://thomasdistributing.com/shop/accupower-2900mah-aa-rechargeable-bat...
And I use this charger:
http://thomasdistributing.com/maha-mh-c800s-battery-charger.htm