I have a NiteRider Lumina 650 that I've taken apart far enough to have replaced the battery. It was easy to open up - three hex screws. The wires running to the battery are very thin, and one had broken off the battery. After unwrapping some of the plastic around the battery I was able to re-solder the wire (with my crappy RadioShack soldering iron) and re-wrap with some electrical tape. Maybe not the safest thing I've done and definitely not the neatest, but it does work, so it wouldn't be terrible to replace one of those batteries if you needed to.