I get about four days of battery life with all of the sensors turned up to maximum frequency, which is every 5 minutes at least for the heart rate. Surprisingly good for such a small lightweight device. I imagine it could go a lot longer if you turned down the sensors to a lower frequency. I found a good rhythm is to charge it when I take showers, that seems to be a good balance and it never comes close to dying. My Apple Watch on the other hand regularly dies before I go to bed, and I can’t wear it for sleep tracking because it can’t last that long.
I will never understand people that pay a monthly subscription to access basic local sensor information like this. Yet I see people wearing subscription-based smart rings all the time. I don’t get it.