Grosh does not run in the background, so it consumes no power except for when you're using the app. It fetches your geoposition briefly once when you start swiping items, so that's a minimal drain on your battery. Grosh disables automatic screen off, so you don't have to worry about unlocking the phone all the time while you're shopping. Of course, having the app open / screen on for a long period of time means some battery drain, no more more than any ordinary app open for the same period of time.