tl;dr Boot to safe mode, restart after some minutes and you should be back to normal!
So a couple of days ago I decided to upgrade my flawless El Capital setup to Sierra OSX 10.12.3. You may say "Aren't you too late for the party?" and that is normally true if it were for other tech upgrades. However since I run on an old hardware (on a MBP 2010 with SSD drives and 4GB RAM) you would definitely emphatise with my conservative approach.
Direct upgrade was plain sailing and to be honest I thought Wow! I should have not been afraid of doing it earlier. But I soon realised that my battery was draining fast. Really fast. Usually I can squeeze between 2 - 3 hours on WiFi and document editing and browsing Safari, and perhaps a couple of days if on sleep mode. Now, after upgrading to Sierra, I was barely getting 45 minutes, and it was not sleeping well.
I tried the usual suspects, namely a PRAM and SMC restart to no avail. After hours of scouring all forums possible, I realised that I was not alone with this issue. Some suggested to go back to El Capitan while others even suggested to take a look at the Activity Monitor and turn off resource hungry apps. The latter did not make sense at all - I would imagine that native apps would be more optimised on a new OSX installation.
... That was until I came across a very unorthodox suggestion to boot into safe mode, use the system for a couple of minutes and then restart. I have an idea as to why, but it worked. I got my previous battery capacity back. These are some theories that I made that could have explained this resolution:
1. Orphan processes that were draining the battery were removed after booting to safe mode.
2. Orphan legacy drivers that were also draining the battery were either removed or fix following a safe boot.
3. Pure coincidence and may have been a combination of resetting the PRAM/SMC and turning off transparency and the usual exotic display features.
What do you think?