I bought a set of one large and one small Lightstick quite a while ago and I use the small one all the time. I bring the small one with me and set it to its max white-light brightness to walk my dog at night before going to bed or rolling the garbage bin out to the road the night before trash day. I keep the large one in my car's glove compartment as a roadside safety device and sometimes use it to charge my phone or DAP in the car. I only top the Lightsticks off every couple months, and only really do it to make sure the battery stays healthy, not because they are fully "dead".
I've never dropped one of them in water, but the little one gets rained on every once in a while. I've never had any problems with either one, and I've really been happy with them.