There is a reason Apple is adding smart charging in iOS 13. Smart charging is essentially going to learn when you usually take your device off the charger in the morning, and it's going to hold your battery at 80% until about 2 hours before that time.
The reasoning? A battery sitting there at 80% incurs less wear and tear. A lithium ion battery gets put under much more stress when it's sitting there at capacity but not being drained at all. It's the same reason why they recommend leaving an electric vehicle at 80% if you're going to go on vacation for a while and not drive the car. 80% is enough to keep its systems up and running while you're gone and not run all the way down to nothing, and it avoids having the battery sitting there unused at 100%. It's just harder on the battery, plain and simple.
That being said, I am not one of those crazy people who only ever charges their devices up to 80%. If I put it on the charger, I let it go all the way up to capacity--life's too short to be micromanaging my batteries all the time and I let the OS do that. But if Apple is adding this precaution into their operating systems to keep the battery lower than 100% for as long as possible, there is probably something to the science.
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Apple more recently added a feature to prevent heavy wear of batteries on devices plugged in for long periods of time.
https://support.apple.com/en-us/HT208710
https://support.apple.com/en-us/HT208710
I didn't realize smart charging also lowered capacity for prolonged periods of being plugged in--that's pretty awesome! But still--that feature isn't in there yet, so anyone who is constantly leaving their iPad or iPhone plugged in is putting undue wear and tear on the battery.
I get it though--I seem to go through almost a full charge a day on my iPad Pro and I hate not having any juice left when I need it for night time stuff.