I bought my Fitbit Blaze (remember those?) in 2016. Battery is on its last legs. I will be heartbroken when it's time to retire this bad boy. : r/ fitbit
Amazon.com: Synergy Digital Smartwatch Battery, Compatible with Fitbit Blaze Smartwatch, (Li-Pol, 3.7V, 120mAh) Ultra High Capacity, Replacement for Fitbit LSSP321830 Battery : Cell Phones & Accessories