My Samsung S8+ has started having periods when it does not keep up 100% charging when connected and in simple editing usage. If I leave it idle it charges slowly and the "charger beep" occasionally goes on and off. (But charging icon is lit most if the time.) If it is turned off it charges fast.
I only use original cable and charger and have replaced these. The problem has ocurred with several different power grids. I am abroad and can not claim warranty.
I had exactly the same problem with a Note 3. Original Samsung service ran the full program on it and declared it ok. (It was 3 yrs old then.) Finally I let unauthorized repair shop change all charging components to no avail.
I barely use a computer any more. My phone is connected to charger and often in heavy use about 18 hrs/day.
Once when I bought new battery for Note 3 (often change these) the original service center insisted on examining my phone even though I considered it OK at that time. They said phones that are connected all day may develop problems. I couldn't leave my phone for examination for privacy reasons.
Note 3 is now bricked by yours truly.
S8+ is 1 yr old and I have never changed its battery. It has started developing this same strange disease.
Maybe I should just leave my S8+ for battery change, but I fear it has developed the same problem as my Note 3. Changing battery was simple with Note 3, but did not help.
I have considered factory reset, but that would be difficult for me now, since backing up would take time. (Could malware or something be running and draining battery?)
Sorry for long post but does anyone have advice? Does SS include "controlled aging" in the software? ;)
Edit: I wrote this long post connected to a stable power grid with original charger. Charging is still 77%, like when I started, charging symbol is lit. When phone was new it would charge rapidly during such an edit. Charging has gone off and on maybe 7-8 times, but it is mostly on.