There are a lot of different rechargeable battery brands available. I prefer Sanyo Eneloops because they loose just 10% of there charge per year. Instead of recharging your batteries before every shoot you can rely on them. Older batteries tend to loose a significant amount of their charge in some weeks and are useless without a recharge after this time.
The common features of good chargers are:
- Handle each slot individually
- Defect detection
Voltcraft Akkutrainer AT3I use this model since many years now. It takes four batteries in individual controlled slots. It is able to tell you the weakest battery in a set of four by measuring the amount of power each battery was charged with. This feature is very useful because the weakest battery defines the power output for the whole set. To charge a set of 2000mAh batteries it takes about 3 hours. There is a discharge and refresh functionality included.
Maha Powerex C9000This is a high end charger. First of all the display is illuminated and therefor readable when it is dark. The charging process is configurable for each slot. You can configure how much power is used to charge a battery and you can configure how fast they are discharged. Because of this you can handle AA and AAA batteries individually. It tells you the amount of power which was charged for every battery. This way you can find out which battery in a set has to be replaced. And since you know the exact capacity of each batteries this works even if you have a set of more then four batteries.
The device is very spacey for a four slot charger. But that's a good thing. Because of this there is a lof of space between the batteries so they don't get as hot as with the other chargers. I like this charger the most. Unfortunately there is just a four slot version of it. I would appreciate an 8 or 16 slot version.
Technical specification you can find here: Maha Powerex C9000
Maha Powerex C801DYou want to charge eight batteries at the same time? Then the C801D is the right device. There are a lot of eight slot chargers in the market but this one is different. Even if fully loaded with eight batteries it charges them in just 1 hour (2 hours in soft mode). This is great! It does not offer much additional functionality. There is one button to trigger normal/soft charging and one button to perform a conditioning of the batteries. As I mentioned before I wish they had build in the very good display of the C9000 into this device. The current display is hard to read and not illuminated. But that's already it with the down sides. If you have a charger like the C9000 this one is a good charger for daily business. Plug the batteries in and wait for the "done" message. No button pressing and configuration necessary at all.
Technical specification you can find here: Maha Powerex C801D