Do remember that I'm replying to a parent comment looking for "a simple watch with simple features". The watches that I'm referring to are basically pedometers and sleep trackers, with Bluetooth notifications from your phone. Of course it's possible to get week+ battery life with that feature set, even with a nice-looking AMOLED display. If you're willing to settle for an TFT-LCD display (I don't recommend it), then you can get nearly a month.
Then additional replies come along, saying, "Oh, but ---I--- need independent on-board GPS and waterproofing to two leagues of depth for my SCUBA hobby, notifications that never ever glitch, and I want a privacy audit trail for all of my super-secret data about how many steps I take per day". Well, okay. Maybe just buy an Apple Watch then? It all depends on your definition of a "smart watch", but I am discussing how I believe that parent commenter and myself define it. If you're incredulous that week+ battery life is ubiquitous in this range, then we may be thinking about completely different things.
What is your current watch? Curious about what model I could confidently recommend to people who have the battery problem.
Honestly, my favorite watch over the past 5-10 years has been a no-name that shows up on Amazon with a search for "EURANS Smart Watch 44mm, AMOLED Fitness Watch". $20, today. Since it uses standard watch bands, it was easy to find an inexpensive steel upgrade band. The phone app for managing this watch is the best I've used, and there were enough decent-looking watch faces available to make me happy. Battery lasts 12+ days.
Unfortunately, I found that with the EURANS, Bluetooth notifications on my phone were sometimes flaky. With Amazfit, notifications are solid, but sometimes syncing steps from the native app to Apple Health can be flaky. In the ultra low-end range, you're going to deal with something, but for me the Apple Health stuff is easier fix with the occasional manual edit.