I brush and waterpolo in the shower. I don’t even use the tank. I just hold a shaving cream lid and the hose together and let the shower hit the lid for a perpetual amount of water; as long as the shower is on. Makes it fussless.
I am sorry, but I cannot answer that. We don't take these one on trips. They are kind of bulky.
However, the most that might happen if the battery dies, you would use it as manual tooth brush.....
Sorry, can not answer your question.