I've always had an iPhone but was talked into a Galaxy S9 which after 3 months I still don't really like. The battery life is rubbish ... I charge it to 100%, and it loses 5% with me just reading an email!!! I've got all background stuff turned off so have no idea why. My partner has the previous version and his does not have this problem. Is my phone faulty???
Unfortunately it's not always a quick fix to problem solve battery worries.
Yes it could be the battery failing however what I would first suggest to do is this in order.
Samsung apply a 24 Month Manufacturing Warranty on their phones so as yours has only been owned for a short period of time you'll have no issues getting support. I assume it's never been dropped and the water indicators haven't been tripped.
Battery output is a subjective topic as many factors can affect usage times / screen on times such as a poor network signal and in some cases sd cards etc and app settings and preferences etc.
I look forward to perhaps viewing your battery stats screenshot if you decide to upload one and hopefully a positive outcome for you.
The Samsung Galaxy s9 is a powerful phone so let's hope you can start enjoying using it as it was meant to function.
I wish you all the best with this situation.
Current Phone ~
Samsung Note 20 Ultra 5G SM-9820 _256Gb SnapDragon 865+
Samsung One Ui 2.5/ Android 10.