Originally Posted by cyccommute
Be aware, however, that rechargable aren't necessarily the best answer to all problems. For example, if the light is going to sit unused for long periods of time, alkalines self-discharge at a very slooooow rate. On the order of years. Rechargables self-discharge on the order of days with NiMH being worse than NiCd (30% vs 20% per month). The Ni chemistries are also of a lower voltage, 1.2V vs 1.5V, which can affect the light you get from a headlamp.
I always use Duracell batteries in my lamps that take them. They have the brand name over here and the quality and the life and the power. Other copies of the high power batteries do not work as good.
I do use rechargables occasionally for cheapness but They have a problem in that they are 1.2v as mentioned by cyccomute. If the lamp only takes one or two then not a problem. If it takes 4 then you are talking about 6volt on the Duracells or 5.2 on the rechargables. This does affect the Brightness of the lamp.
Still- What do I care as I have just got my new powerfull lamp with Lithium- Ion battery. Pity that that will only have a life of about 3 years before it starts to deteriorate.