Iphone 11 PRO, phone suddenly shuts down and battery gets decreased
Hey guys, I asked same question in "using iphone" part but I guess it fits here better and don't know how to delete it from there so sorry for that. So I'm writing on behalf of my friend as she doesn't have account here. So she has Iphone 11 PRO with 15.5 IOS. Phone recently started to act weirdly, suddenly it can turn off itself and after we launch it, battery get lower by 10-30% comparing to time before shut down. We checked battery capacity but it shows 100%. At first I thought that maybe battery is old and needs replacement but with 100% capacity I'm not so sure anymore... Anyone had problem like that and knows how to fix it?
Here are two pics of battery, as you can see on this red bar, suddenly it went down so much, it was moment when device shut itself down.