Why does my iPhone 16 Pro Max charge beyond 80% despite setting limit?

Apple notes in their documentation that the battery will charge to 100% "occasionally" to help with accurate battery calibration.

The big question here is how often "occasionally" might be. When I tried this, occasionally was 3-4 times a month. Some users report more activity and some less.

Frankly....and this is my opinion after trying charge limits for a few months......I think the limit option is more of a gimmick than anything else.

I've gone back to regular Optimized Battery Charging with no limits and I connect the power adapter to the phone at night and leave it connected all night......every night.

The battery starts at 100% each day this way, and I don't have to recharge the phone later in the day as I usually had to do using the charge limits.

With charge limits, you have to charge the battery more often.....and that counts as wear and tear. If another user can get a month or two more battery life using charge limits, I could care less. The phone does what I want it to do using Optimized Battery Charging.

Perfectly normal. The Apple Support article on optimized charging even says the battery will occasionally charge to 100%. The article doesn’t say, but I suspect it does that to recalibrate the battery health percentage displayed. As chemicals age they no longer can hold the same milliampere charge.

The apps you named are three of the most bloated, inefficient and power hungry apps you can use. There is no motivation for either Google or Facebook to spend the time and money to improve the efficiency of the app. Read a book, you battery will last longer.