Interesting. I'm not seeing overnight drain on my XS Max, much like with my iPad Pro. On the other hand, my Android devices with the same setup - phone connected to LTE, WiFi on - do lose a few percent overnight.
It's the way the battery is calibrated and how the phone charges. When plugged in and on, once the battery reaches 100% it stops charging and starts draining as normal. Once it goes down a percent or two it starts charging again. The battery is calibrated to read 100% when in the 97 to 100% range. That way you don't freak out when you wake up and it reads 98 or 99% when it's been charging all night.That's also why it takes a long time to go from 100% to 99% when using as you're really using 3% or more. So yes, even when on the charger all night, the battery will drain slightly. With that said, I highly doubt this rapidly degrades the battery as that other guy said.
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