Note it can vary depending greatly on settings, which is kind of nice. I have a Forerunner 745 (sweet spot of features and price on Prime day), and I can get,

Note it can vary depending greatly on settings, which is kind of nice. I have a Forerunner 745 (sweet spot of features and price on Prime day), and I can get, IIRC, a solid week plus with the default settings. I ended up dialing way up the settings to get better tracking of sleep, which took the battery life to around 2.5 days.