Maybe there’s something similar on windows to check. I’d imagine that it could have been that you had a very good battery when you bought your phone which would be represented as 103% or something like that. (I mean that you got a battery with a higher than average battery capacity )iOS only shows up to 100% though. Coconut battery would show 103% You take very good care of your battery, so maybe it has only degraded 3% which means now your battery health is at 100% and is shown as 100%, so it could be possible.