Your iPhone will charge to 85% if I'm not mistaken. Once there it will slow charge to 100%. After that if still plugged in it will stop charging again to keep the battery from overcharging. It will keep going through this cycle as long as it's plugged in. This is the way it has been with iPhone's.
It is no different as Zerog explained when you charge a motorcycle battery which until recent was the business I was in. It will burst charge it to 85% then go into a trickle mode and it's main purpose other than overcharging which with these new battery technologies are quite hard to do, It also keeps them from overheating which would degrade the battery more than anything else no matter what kind of battery. Zerog is totally right but just thought to throw this in and now you got it all. One last thing, As long as it remained plugged in it is going to stay at 100% until you remove it from the charger anyway so it will stop charging and remain in a dormant state anyway.
Ok so what is the argument if any? 5% here or there from what am saying backed by the info Zerog reported is no big deal. I agree with everyone including you so there is no big deal here. Everyone who answered is correct, There is no wrong here and thank you for providing the link.I'm just going by what apple's site says
https://www.apple.com/ca/batteries/#mn_p
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