I sometimes see the unit stay at 98% or 99% for a long period when I am charging it. But usually, when I start the unit up again, it shows 100%. I wouldn't worry - this Edge model has the best battery life they've ever offered to bicyclists.
After about two month my new Edge Explore (2018) behaved just like that. In my case the cure for the seemingly 97% maximum battery charge level was to discharge the device to zero % and then charge it overnight. In my case the battery charged to 100% again. After shutting down and at first power-on the next day the 100% was still there. The device discharged as quick as possible with the display staying on with 100% brightness and with GPs satellite search enabled, keeping the device far from the window to prevent getting a gps-fix (possibly searching consumes more power). Worth a try? Possibly a different cure is a full hard reset, but you loose all settings and maybe your personal data. So backup those first.
