I second the Amazfit Bip. Mine lasts around 40 days per charge as a watch, heart rate, and step tracker. I leave notifications off.

Thirded. I get about a month between charges with everything turned on (notifications - the main purpose of the device for me, as well as heart rate monitoring, step and sleep tracking). Its no Pebble in terms of functionality or third party development, but I had Pebbles since the initial Kickstarter and while initially I installed every app I could find and tried to use it for anything and everything, eventually I worked out that (for me at least) it worked best as a extension of my phone display, not a replacement.