The problem with most of the rechargeable NiMH batteries is, they don't retain their charge over a long period of time. They are designed for our devices that eats batteries, like digital cameras, and other things we use. They usually don't work for more than 6 months in low power consumption devices like remote controls. But what about Emergency Preparedness, do you really have the time to charge all of your batteries so you can use them, right before you need them?
Newer technology has changed the way NiMH batteries are built. Current NiMH batteries have an internal resistance that drains itself even when not being used. New NiMH batteries now have a thin film used during the manufacturing process, that cuts down that internal resistance tremendously. Because there is more material in the battery, there is a slight drop in overall charge capacity, but when it will retain 85% of its charge over 1 year on the shelf, I will make that trade. Plus, you dont have to purchase any new chargers, they will work in your existing NiMH chargers.
Other advantages of these newer types of NiMH are, voltage is more stable, reduced heat buildup when the battery is quickly charged or discharged, higher efficiency, and higher instantaneous current discharge capability.
Cost differences between the older and newer types are not much different. I can purchase a 4 pack of Duracell AA w/2650 mAh capacity for about $10. While the newer type equivalent, but only 2000 mAh, around $15. But when you weigh the fact that after 3 weeks, both types would have the same capacity charge stored, it almost a no brainer to use the newer type of NiMH.
Update: I found Wal-Mart selling these Duracell Batteries for about $10 for a pack of 4. Kodak is also selling Hybrid batteries. However, Energizer isn't doing anything with this technology.
These newer batteries are labeled as one of the following:
I wanted to share this information with the Ham Radio community because I recently rebuilt a battery pack, with NiMH batteries I purchased at a local store, and thought about the problem with the short shelf life. If I want to use my radio at a moments notice, I wont have a battery pack already charged. That is a problem, because you don't always have a way of charging your gear when you need it.
Wikipedia - NiMH
Wikipedia - Low_self-discharge_NiMH_battery
Duracell - Pre-Charged
Rayovac - Hybrid