Apparently Fitbit Charge HR's have a common problem where the part that holds the charger onto the back of the Fitbit breaks and comes off. A friend of mine was tired of trying to get support to replace hers so I designed a 3D printable one. I won't say it's perfect but it gets the job done. This is the smallest object I've ever designed but Tinkercad was up to the task. Instead of designing a separate side button, I embedded it into the clasp, since I'm printing it in PETG and it's quite flexible. It serves as a nice tab to hold the clasp onto the fitbit if you're not ready to glue it on. Just make sure to hold the sides when attaching and detaching the charging cable to it. If you glue it, don't glue the button side to allow freedom of movement. Speaking of PETG, it was quite difficult to print this size reliably using PETG since half the time it stuck to the nozzle and became a big blob and when it was successful there were strings galore since retraction moves didn't have room to escape the area. Let me know if you have better luck with ABS or PLA although I'm thinking that nylon would be the best material.
Let me know how the button works. I may attempt to create a separate button if it doesn't work as well when glued on to the fitbit.
Monoprice Maker Select 3D w/ Duplicator i3 Melzi 4.4 board
Doesn't matter. It's 1mm wide.