My Charge 3 did this today. Warranty was up three weeks ago. Fitbit had every right to deny to replace it, but 10 minutes with tech support chat and they are shipping
Fitbit Charge 3/4 Screen Protector (6-Pack)
Amazon.com: Fitbit Charge 3 Fitness Activity Tracker, Graphite/Black, one Size (no fitbit Warranty Support), 0.06 Pound : Sports & Outdoors
100mAh Battery For Fitbit Charge 3 High Quality Replacement Accumulator - AliExpress
Amazon.com: Fitbit Charge 3 Fitness Activity Tracker, Graphite/Black, one Size (no fitbit Warranty Support), 0.06 Pound : Sports & Outdoors