My phone died then I charged it till it was at 100% and is now draining slightly fast

[Android Central Question]

I fell asleep and my phone got unplugged while I was asleep I first thought “oh crud.” And I plugged it in and I assume it died around 2am or maybe just before I woke up in other words it was dead when I worked up. So after I plug it in I waited till it was at 100% a bit less 2 hours later with auto brightness and regular brightness on low and on airplane and only one app open (Spotify) since I was at place with no WiFi. (Typing this using an iPad which does have WiFi since it does but I don’t have the password to it) I mean it stopped going so fast but it’s still a tie bit fast at first it was like 100 and 30 miunutes of not being on its charger it was at 30% I thought “nothing to worry about.” Them 80 and then 77 I’m a blink of an eye and is now at 52% as I type this. Anyone got any suggestions. I heard about charge cycles if my phone goes down to 0% but this is the 1st or 2nd time it happened.

Furthermore when I plugged it in after it’s been dead it shot straight to 36% or 38% I can’t remember.

Should I get a new battery or let it readjust somehow to keep charging it to 100% and pretend it’s not an issue.

 

[Rukbat]

Keep charging it to 100% (that means leaving the charger plugged in for 30 minutes after the phone reaches 100%) for a few charge cycles (and never let it get below 40% before recharging it). If it doesn't clear up, you need a new battery, but it may clear up (at least if you don't discharge it below 40%). The battery might be throwing a dendrite (shorting it) at 36% - but if you charge it at 40%, that doesn't matter.