By the way, for whatever it's worth, I'm much less picky about tail lights. I have a Planet Bike Superflash and a Cygolite something-or-other. The former uses alkaline or NiMH AAA cells. The latter uses an internal USB-rechargeable LiIon battery. They both go for weeks without needing care. They cast enough light and are convenient. I have a dyno powered taillight on only one of my bikes, and I sometimes supplement it with one or both of my battery tail lights. I do that because it's easy, not because I'm convinced I need to.