[crdb]

My Amazfit Bip ($99) is supposed to have 45 days and lasts about 30 days on minute heart rate monitoring intervals (based on a month and a half of trying it).

I wanted something a bit smaller, to fit under the shirt cuff, so got the Mi Band 3 ($50) which lasts about 10 days (probably 20 days if you don't allow it to display notifications and set a higher HR interval).

The Mi app is pretty bad, which forces you to buy an extra app (for me, Notify & Fitness, for Google Fit sync).

[ValentineC]

I second the Amazfit Bip. Mine has around 40 days of battery life.

On iOS, I use AmazTools [1] to sync the heart rate data to the Health app.

[1] https://itunes.apple.com/us/app/amaztools/id1386033880?mt=8

[calgoo]

In regards to the Mi Band 3, there is an app called Mi Band Master, which works a lot better then the original. It exists for both Android and iPhone. I use it for sleep monitoring, and notifications. Battery lasts for about 2 weeks.

[mehrdadn]

Huh, interesting, thanks for the pointers! 45 days might be bearable.