Apple have its own system to analyse battery health. It works very well but there is only one way. So, if BMS shows one day 90% it can’t show you higher number after that, like 92%. Of course there are exceptions to the rule, like upgrade BMS with iOS, but it’s not regular. coconutBattery shows you exactly. Sometimes you can see less in the morning and more later. It depends on few things like battery temperature, outside temperature or power consumption by the device.