There's also the possibility of using Advanced Charging Controller - though it requires root. Essentially you can set it up so when the battery reaches eg. 100% it stops charging, and resumes only once it reaches eg. 15%. Surprisingly the Android devices that I have still don't ever stop charging on their own, constantly keeping 100%.

[Advanced Charging Controller (ACC)](https://github.com/VR-25/acc)

[BU-808: How to Prolong Lithium-based Batteries](https://batteryuniversity.com/article/bu-808-how-to-prolong-...)

I do this with my tablet: It is running Fully Kiosk Browser, reporting to Home Assistant. When device reaches 20%, it turns on Oneplug usb relay and turns it off at 80%.

You can do that, but you still have a battery that will eventually become a problem. I prefer my wired devices not having a potential bomb on board :) As I generally use old devices with worn batteries this is likely to become a problem much sooner, and much less of an issue to stick a screwdriver in and start tearing parts out of the device. Of course you're not going to do this to your brand new tablet under warranty.

However, doing that you do have the benefit of having "UPS" protection of course (how much depends on the charge cycle). In my case this isn't really a problem because if my power is down there is not much in my home left to control that still works.

Yes, and yes laptops prevent this now. My lenovo thinkpad actually stops charging and lets itself discharge all the way to 20% before charging again.

Mobiles and tablets generally don't do this because they are almost always used in a mobile manner. With the exception of the special battery protection in iOS that was mentioned in the article.