I bought a Charge 4 recently to use when I run or bike. I bought it to replace an old Fitbit Surge that served me very well. However the Charge 4 is another story since the screen is unreadable outdoors. It doesn't even have to be full sunlight. How absurd! Selling a device that has biking and running functions but cannot be read outdoors. I am currently fighting with Fitbit to get a credit towards a different device.