Which fitness tracker has the longest battery life?

Among these picks, Xiaomi advertises up to 21 days for the Smart Band 10, Amazfit claims up to 14 days for the Bip 6, WHOOP claims 14+ days for the 5.0, and Garmin claims up to 11 days for the Venu Sq 2. Fitbit's Inspire 3 is rated at up to 10 days. Reddit threads (r/amazfit, r/miband) generally report real-world numbers somewhat below the marketing claims, especially with always-on display or GPS use.