Comment by CWuestefeld

My Instinct 3 Solar shows 34 days remaining in the battery. I charged it sometime last week, so we're talking about upper 30s at least.

That's with running activity tracking including GPS for about an hour a day, and continuous heart rate monitoring.

At least on my device (and my body) the spo2 sensor is very finicky, requiring absolution stillness, and even at that I don't think it's accurate. So I don't use that.

I also discovered recently that simply using a custom watchface - even one built with an eye toward efficiency - lowers my battery life to about 2 weeks. The native faces enjoy privileged operations and are thus highly efficient. But custom-coded stuff apparently runs in a sandbox that has the effect of costing much more power. That's unfortunate, because my custom face used custom high-legibility fonts (derived from what's on interstate signage), making it noticeably easier on my aging eyes. The built-in fonts aren't great for this.