The car does this for some reason. I suspect it’s some sort of predictive algorithm that determines how much to overcharge to ensure you have the set charge the next day. It appears to change from time to time for whatever reason, sometimes my car is stops right at the limit, other times it charges a percent or two past. Sometimes it will use that extra percent or two by the next morning since the car can stay awake for hours after charging in some situations. Either way, it’s not too big of a deal. Based on all available evidence, the battery is more likely to have an internal failure that renders it useless before the degradation is bad enough to warrant replacement charging to even 80-90%.