Been away from this page for few weeks.
Now I'm enrolled for OnePlus 6 Open Beta 9.
They added a number of small, yet significant, changes with this update where OnePlus has updated the Android security patch to December 2018.
Within 48 hours of trial, the battery performance for my phone is slightly improved. Some say that the social media apps affected the battery life performance. However, as for now my phone able to survive for almost a day and half (do take note that I am not a gamer thus no gaming mode is turn on and no game installed).
Still figure out on how long the battery and stay up.