Battery drains fast under 15%

[Android Central Question]

I have a Samsung Galaxy S8 that I bought half year ago. It worked perfectly fine until I discovered that it the battery wouldn't last long after it reaches 15%. it would last couple of minutes and then it shuts down. I put it to Max Saving mode once it reached 15%, at that moment the battery percentage was still 15% but after a couple of minutes the battery percentage dropped to 0% and still worked. And during the night with WIFI turned off, all the background apps closed, it drops like 10%, while when i bought it dropped only 1-2%. I don't know if it's a battery problem or the phone needs a calibration, but when I get to school I shut it down (because we're not allowed to have our device turned on during lessons) and when I finish my lessons I turn it on. I though this could be the main reason why my battery drains so fast below 15%.
Could someone tell me the problem and how to fix it... thanks.

 

[belodion]

It could be a bad battery. It may be replaceable under warranty.
See also this:
https://r.tapatalk.com/shareLink?sh...tral.com/showthread.php?t=500054&share_type=t

 

[Mooncatt]

I also suspect the battery.

For future reference, it's not good to run the battery that low. It's best to keep them between 40-80% for maximum longevity.