I sue my urbans on low whenever possible .... normally they are bright enough for safe riding. But ... i have to have two. No battery swap possible.
When I get my CREE set-uop working I might be able to bring one light and a spare battery.
I am pretty sure the Urbans use the same rechargeable battery (my old Lezyne did) and if the Urbans ever die, I will find a way to replace the batteries ...If the factory can do it, so can I. Then I will bring spare batteries .... but the two-light setup is awfully nice for high speeds/bad roads.