Yes, you can change the battery, but this procedure intentionally involves deinstalling the light. The batteries are Lithium Polymer - just like your cel phone and the lifespan - several years - should be similar. So ideally you should not have to change them out through the normal course of use.
We are also hard at work on charging solutions. These lights represent the best useable, efficient, and reliable technology available at this time. We hope to have new and efficient supporting charging technology in place over this next year.