Optimized Charge Limit
You’re probably family with Optimized Battery Charging. Your Apple devices use this feature to learn your charging pattern so they can charge slower when you can wait or faster when you’re about to head out. This will prevent your battery from aging as quickly.
Now, Apple introduced another feature called Optimized Charge Limit. This feature learns your daily usage to determine when your Apple Watch can be charged to the right limit or when you’ll need a full charge.
As soon as you update to watchOS 10, this feature will be turned on by default. You can disable it by going to Settings > Battery > Battery Health and turning on or off Optimized Charge Limit. If you have an Apple Watch Series 8 or older, you’ll need to disable Optimized Battery Charging to disable this feature.