erwinallamby, You can check the 1st 2 links to see if the info. helps gain back battery issue and if no help then faulty battery may be you issue.
If the smartwatch only powers on when connected to the charger regardless of charge time, then the battery is faulty. Replace the battery using last link guide.
https://us.community.samsung.com/t5/Wearable-Tech/Gear-S2-battery-life-SUCKS-after-recent-update-for-gear-s3/td-p/49290
https://www.youtube.com/watch?v=jR1w9DD_5sY
https://www.engadget.com/2014/04/09/samsung-galaxy-gear-2-teardown/