Does anyone know how the battery life works for this? GPS takes more battery than anything else. Lets say my friend and I each allow viewing of one another. Does my GPS run in the background the entire time I allow people to view me? Or does it only activate when he opens the app and views me? In addition, if he has Find Friends open in the background, while it continue to drain my battery? I'm trying to figure out how I should use this. I'd really like to be able to continually use it but if allowing people to view me will drain the hell out of battery I won't. Any ideas?