Theres probably a small battery built in that stores some profile data from settings you configure so that it doesnt get reset every time you change batteries.

Id put a battery in...

---

Strava

I figured as much and was planning to put a battery in... but found it odd that I couldn’t find out anything about this.

Different issue but what I learned about my Tickr this month was when you change the battery pay close attention to the ring gasket (or whatever it's called) and how it mounts around the battery compartment lid. I vaguely remember just kind of "tucking" it back into the compartment, not realizing it had come off the lid circumference. 2 weeks post change of weird, and worsening, HR readings lead me to swap battery thinking it was a dud. Battery was corroded out badly on one side from sweat penetration.

Turns out that the simple explanation is that I’m an idiot!

....battery is there....but clipped into lid....I opened it 4 times and looked in the compartment without looking at the lid!

Sorry to waste people’s time.... I hope someone gets a laugh!

Not quite a laugh but I smiled ;)