iPhone 11 Is this normal: Battery Health Still 100%

[dz5b609]

A voltage issue that discharges the battery from around 40% to 10% in seconds?

Yes, because it doesn't actually goes from 40 to 10% in seconds (which isn't really possible anyway) but the voltage isn't stable which makes any battery readout do weird things because they measure battery by partly looking at voltage. Which is why it can go from 40 to 10 and then for example immediately back to 80 when you plug it in a charger.

 

[MikB]

This refurbished iPhone 12 Mini has been in my hands close to 20 months now and claims it's at 100% capacity. …

This unit since 12 months or so displays power problems in that once charge goes down under 40%, it can die without warning. Typically it can start once again, but now charge is 10% and soon it dies completely. When recharged it's back to normal. When I started using it this unit could run down to under 10% without problems. Occasionally it still does, but this is rare. …

Except for dying on me when I cannot charge it, it has some volume issues, that may or may not be related to power issues. Otherwise will work fine, as long as I keep the charge topped to 40-80%.

Recently I got this 100% health battery replaced by Apple. All those old problems are gone since I got it back. I gained one new problem in that quite known blurry picture thing, that is now more prominent (not sure I had it before). I suspect a magnetic case there. The fact this seems to be app dependent indicate it's an iOS thing though.