Samsung phone charges poorly, periodically 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.
The phone probably had malware introduced through a SIM-card.

The phone also stopped recognizing the SIM-card. No calls or data possible. It asked me to make a factory reset to "accept new network configuration". Charged poorly when not turned off.

I removed the SIM, made backups and factory reset (which needs wifi to find my Samsung account password to allow for reset).

I do not wish to point out any country in particular. This has happened before in other countries. The new SIM that only worked for two days, I had bought in a big shopping center that also gave away SIMs for free with other buys. Largest network in the country I believe.

I had also connected to a hotel wifi with advertisments etc.

I went to the only direct outlet for the network and asked. They told me the SIM had given me the problems. Hotel networks have ads but are safe.

Malware was running, draining power and also interfered with connection.

The network shop was super pro. They sold me a new SIM and "pocket wifi" and set up everything perfectly. All works fine now.

My conclusion:
Only buy SIM directly from the network shops (or if you trust their envelope seals). (A lot of hassle for me that often travel and roaming  becomes too expensive. But no other choice.)

Data I backed up but apps seem to have problems downloading through the Google/Samsung system. Hopefully it will improve when wifi is not crowded in the night. But I can restore apps manually. The app data seem to be there if I just download the app manually. The nice Adobe Lightrooom that I reinstalled suddenly has pay-options for what used to be free :(  ;)

What the malware programmer wishes to achieve is not clear.