My battery also drain very quickly. For example in this case, see how quickly the battery percentage fell down after I had the phone in flight mode and used it a bit.
following that I connected it to a power source, but when I used my phone again it depleted very quickly:
EDIT: Also I just took this screenshot to show the Wifi Indicator, but I just noticed that it’s been only 2 hours that I unplugged my phone and it already used 20% of the battery, now calculating that 6hours would be left with the current charge. 8hours? come on!
EDIT 2: see below how the battery decreased around 20% this morning after around 30minutes of usage. Before I had it on flight mode over night.