Mainly I want a dynamo for a trouble-free commuting bike. I get tired of worrying about which batteries I charged or need to be charged. It makes more sense to be able to get on the bike, start pedaling and turn on the lights. Also I've been experimenting with home-built high-power LED lighting systems lately. I've been pretty amazed at how bright a 3-watt Luxeon Rebel LED can be, for instance. I hope to run two 3-watt LEDs off the typical 6-watt dynamos I've been shopping for. If I used batteries for a similar lighting setup I would be recharging batteries nightly.