I do not know nor do I care what it is as my watch was bought in the same time frame as yours and it is 100% battery health. I just want my settings I had before an update to remain the same after an update. I bought this watch to use and I fully expect to get at least 6-7 years out of it and then I will go with a battery replacement and keep going.I have had this happen on my AWU2 since update to watchOS 10.5! The watch is 235 days old (since OCT23) and the battery is at 100% health. I wear it 24/7 except for charging (about every two days due to the sleep sensors needing a battery charge of >30%). My question to you is how long can you leave optimized charging turned off without affecting the life of the battery in general or for your use case? TIA!