I have an Apple Watch 6 Nike and I’m experiencing the same problem, but even worse than what is happening to you. I bought my Apple Watch in June 2021 and the battery health has been 100% until October. Now it’s 92%. Last week it was 96%. Idk how it’s possible, but every two or three charges the battery health dropped by 1% for the last month. And of course I use the original charger that was in the box, and as power brick I use the one that came with my Apple Watch 3 Nike. If anybody can help me, pls reply to this post, cause I have calculated the battery health that I will have next summer, and if it continuous this way it will be 60