Apple Watch Ultra 3 battery optimization issue
My Apple Watch Ultra 3 has battery optimization turned on and it charges to 100% non-stop.
Apple Watch Ultra 3, watchOS 26
With battery optimization turned on, it still may take some days to weeks for the watch to learn your patterns. It adapts its charging behavior to your patterns of use. (This is also true to some extent with iPhones and Mac laptops, but in different ways.)
Charging to 100% and staying at 100% for extended periods can shorten a battery's lifetime. Hence with the watch, it may stop charging sometimes at 80%. However, if your pattern of usage is such that 80% would not enable the battery to last through a normal set of activities and use, it might "decide" to charge to 100%. As an example, if you sometimes run the watch down to 15%, 20%, 30% in normal use, the algorithm might elect to charge past 80% to something higher, maybe 100%, so you would have enough battery in normal use.
I noticed this with my watch (Series 11), which is only about 6 weeks old, so I am still observing how it behaves. But after quite a few days where I never was below 50%, my watch started charging just to 80%. But then I started using it more, for sleep recording and multiple workouts per day, and it started to run down to about 30% or sometimes lower. I noticed then that even with optimized charging enabled, it now sometimes charges to 100%.
Just today it was down to 39% so I put it on the charger and it went up to 100% very quickly. Other times it stops at 80%. If, in your normal use, the battery is being "exercised" and is often down at 50% or lower, I think Apple's algorithm might elect to charge to full (100%) depending on the usage pattern and the time of day. For me, sleep tracking requires around 20% of the battery over 7-8 hours and I think the battery notices that and factors it into its charging pattern.
Based on what I have seen with the iPhone and Mac laptops, it can take some weeks or even months for the device to "learn" the optimal charging pattern for a specific user's pattern of use.
