Originally Posted by steveknight
the problem with using rechargables is you loose a fair amount of brightness because of voltage drop. you start out with only 2.5v and go down from there. in blinkies I use li on cells they are higher in volgage and mainting that ligher voltage to the end. the brightness is noticable.
NiMH do have a lower nominal voltage than alkalines, but like lithium cells they maintain voltage much better over time and under load. So yes--alkalines are initially brighter due to higher voltage in an unregulated circuit, but after the first couple of hours, the NiMH are still plugging along at 2.5 volts, while the alkys are slowly fading beneath that level.
I run multiple rear lights, and despite the above, like having alkalines in one of them. While they do run dimmer than the other chemistrys for most of their lifespan, they don't fall off rapidly. Both lithiums and NiMH drop off rather suddenly--not a good thing in a taillight since I won't know until I'm home or I'm squished.
I used to run lithiums, and while they last a long time, they're still too expensive for me. I do carry a set in my seatbag for emergency backup though.
Jack