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.
They come in different sizes and they don't necessarily correspond to standard USA ring sizes, so it takes some effort to measure and make sure you get the right one. But the effort is worth it to get a comfortable fit. And they are cheap enough that you can always buy multiple different sizes. I think I paid like $11 for mine on Taobao with free shipping (part of that may have been a discount since I was a new customer).