Update: Jan. 2021 - Changed link to point to Eneloop Pros. Removed dead link for charger
Back in October, I wrote an entry about better rechargeable batteries I had recently discovered. At that time, I hadn't bought any, but I finally got some before the wedding I shot back at the start of March. There are a few different brands out there. The ones I got are from Sanyo. The brand name is Eneloop, and they rock.
After living with them for a few months, I'm happy to report that they work as advertised. The key feature that makes them valuable is their low "self-discharge" rate. The previous sets of rechargeable batteries I've used apparently had a much higher rate.
Basically, what this meant is that if you charged the old type batteries and then didn't use them for a little while (say a week or two), they would have lost a lot of their juice. When you put them in, say, a flash to do some photography, you could easily be in trouble. So, in order to make sure they were ready to work with, you effectively have to charge them the night before you want to use them to make sure they were topped off.
These newer versions with their low/slow self-discharge hold onto their power much longer. Their marketing state that if you are simply storing them, they will maintain 90% of their charge for 6 months and 85% over a year. I haven't had them long enough to figure that out, and frankly I'm not really going to try to test it. What I'm interested in is if they ready to go when I need them.
I can deal with charging them if I know I've got a lot of shooting to do the next day, but it's when I haven't shot for a few weeks and I just want to fire off a few shots that is the real test. I just put a set that was charged three or four weeks ago in a strobe and it charged as if a completely fresh set was in them.
I highly recommend these for everything except smoke alarms (just in case).
The more batteries we can keep out of land fills the better off we'll all be. You can purchase them from Amazon and I'm sure other places have them as well.
The batteries come in at least two flavors: "800 mAh" and "2,000 mAh". Make sure when you're getting yours you get the highest "mAh" available at the time (currently the 2,000 version). Especially if you are going to use them in a flash or digital camera.
While this rating isn't as high as some of the other rechargeable batteries out there, the fact that they hang onto that charge for a long time is more than an even trade off.
You don't have to worry about the mAh difference that much unless you are really an intense user. For example, I shot an entire wedding (roughly 1,500 frames) and only used two sets of the eneloops in my main flash which was shooting into a lumiQuest most of the time. So, they work great from that perspective as well.
As a final note, if you want to get a better charger than one of the basic ones, the La Crosse Technology BC-900 is expensive, but very nice. Advantages include the fact that it allows you to charge batteries at different rates (to help them last longer), "recondition" them if they are behaving badly, and also reports when the batteries are fully charged so you don't have to guess. Most folks probably don't need those features, but it's certainly handy.