Thanks. Somehow the ZIP file downloaded is prefixed with "20161201xxxxxxxxx" and the website also cited 1 Dec 2016.
Anyway, I took the plunge and updated my phone's firmware to B05. Other than the poor language and slight confusion in the instructions provided, the upgrade process is very straight-forward and smooth.
Shortly after the update, the phone runs hot and lagged considerably. After a while, it behaves normally. I am on new firmware since noon and so far no issue encountered.
I do notice that the phone latches onto 4G (or even 4G+) network quite quickly now. It used to stay on 3G most of the time. I am on Singtel network.
I will check on the overnight power drain tomorrow morning.