Major battery drain on S6 edge plus

[AC Question]

h t t p :// imgur . com /a/k8VhW (screenshot taken today)

I live in Singapore and I bought this phone in Oct 15.
I'm using Samsung s6 edge plus and this battery drain issue have been happening since 3 weeks ago.
I've tested a few times, charged it to 100% before I sleep, and when I wake up, it's left with approx 20-30%. Never has this issue happened to me before. Battery was working fine all along.
I've tried booting to safe mode and even reset it to factory default(wipe) and even tried clearing the cache. But it still drains significantly. I've even tried putting it to power saving mode plus airplane mode both together at about 40% battery. But when I wake up, my phone battery is dead.
5 days back, I sent this phone for service because the warranty is still valid. They told me they detected some abnormalities with the battery and changed it, but when I get it back, battery still drains.
I have very little screen on time (less than an hour) and the battery can be drain completely... May I know what's wrong with my phone?
Please see attached.