I think this page is helpful:
http://eddys.com/site/page.cfm?PageID=493
I have the EL-500a and use it for urban riding. It's interesting though because I also have this flashlight, and it illuminates better than the EL-500, even though it is smaller and uses just one battery:
http://www.flashlightreviews.com/reviews/nuwai_q-3.htm
This says to me that the electronics on inexpensive bike lights could easily be improved at little cost.