None. I’m one of these oldtimers who has that backward opinion that a thing has to do one thing, but that very good, so I wear a brick of steel that’s actually ticking away that I have to check once a month, if it’s on time. Plus every 4 years it’s gotta have an oiling. On the other side: no batteries to charge. And my fitness tracker is my fat belly ;) kinda fit, kinda fat.