A friend asked about using NiMH batteries for the first time, and why they don’t seem to last as long as expected. The brief answer is that the batteries need to be charged, discharged, charged, discharged, etc a couple of times before the full potential of the energy stored is realized. You can do this through regular usage, or by having a special charger/conditioner do it for you. I generally prefer to cycle through regular use — but realize that your battery life will be relatively short the first couple of times you use the battery and will get better with more cycles. The general life-cycle of a Japanese made NiMH cell is roughly 500-700 cycles before they need to be replaced. You will know when to replace them when charging doesn’t add much life to them.
Here is a decent link to a set of FAQs on NiMH batteries by Thomas Distributing. I used to have a set of my own, but that went down with the site www.askme.com and I’m too lazy to type them out again unless necessary.