I'm not sure what the point of the question is. If it's that tablets and phones are harder to service, it's a fairly well known fact. Although some non-apple laptops are fairly hard to service, too. I'm thinking of some HP Elitebook models we have at work (not sure about the model number).
However, my point was that the issue wasn't related to the devices being plugged in all day long but to the overheating. I don't think a device used as a display would be particularly taxing on the CPU to have it heat up. For example, I've used both the tablet and phone to watch videos for extended periods (>2h) and they got barely warm.
In my case I don't think it was related to overheating at all as apart from being charged all the the time it was used utmost 1 hour a day for YT although battery did loose its ability to retain charge within couple of months(from being perfect) once I started to use it as secondary monitor.
This happened with my iPhone 5c too, which I used for displaying terminal(But removed before bulging).
Newer Apple devices/iOS supposedly prevents overcharging, that might also explains Sidecar integration with macOS.
I can't comment on the behavior you noticed other than saying that the devices seem defective to me, but I may be wrong.
> Newer Apple devices/iOS supposedly prevents overcharging, that might also explains Sidecar integration with macOS.
I'm not an expert on Li-Ion batteries, but my understanding is that this is a separate issue.
What this does ins't preventing overcharging, it just charges the battery less than what it's fully rated for, the idea being that you'll probably not need the full charge, hence the description of that iOS feature saying it tries to learn when you use the device to know when it needs to be fully charged.
My understanding is that LI-Ion batteries may see less degradation if they aren't always charged to 100% of their rated capacity, especially if this capacity is "pushed too far", for example by manufacturers looking to extract the longest possible advertised battery life for a device with the smallest possible size. This is something that I expect most phones and tablets to attempt to maximize.
Overcharging would mean, to me, attempting to keep on charging the battery once its rated charge has been reached. The point of my original comment is that I don't believe that leaving a device plugged in after it says the battery is at 100% would keep on trying to charge the battery, as was the case for example with "dumb" NiCd and NiMH chargers. The battery control circuitry would stop charging once it deems the battery full, so leaving the device plugged in would simply have it use the power from the mains instead of from the battery. Which should actually help with battery aging, since it eliminates "useless" cycles (useless because the device doesn't need to work on battery since mains power is available).
A problem is that almost all smartphones/tables don't support charge limiting feature. Business laptop like ThinkPad and competitors support to set max % of battery charging rather than 100%. It significantly increases battery life.
Any idea why that is? Somebody on Quora suggested it was mostly about people not being able to figure it out, which I'd believe. Plus some guesses about the way people just change their phones frequently enough for modern batteries anyway.
