vívofit Owner's Manual - Replacing the vívofit Device Batteries
Tutorial - vívofit jr. 3 Battery Replacement - YouTube
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Amazon.com: HQRP 4-Pack Battery Compatible with Garmin Vivofit Vivofit-2 Activity Tracker Fitness Training Computer (2 Batteries fits Training Computer + 2 Batteries fits Heart-Rate Monitor) 010-01225-00 : Electronics
Amazon.com: Garmin vivofit jr. 3, Fitness Tracker for Kids, Includes Interactive App Experience, Swim-Friendly, Up To 1-year Battery Life, Digi Camo : Sports & Outdoors