There could be other causes but give it a try at 50% or 40% and see how much difference it makes.
You would have to check with Task Manager or Resource Monitor to see if other processes are using resources and consuming battery life. In Task Manager sort the CPU column in descending order ... the top CPU users will use the most battery of the running tasks. Sometimes you find something you didn't expect. Likewise Resource Monitor can show you the top Disk users, Network users, etc. Memory usage isn't necessarily an indicator of battery usage.
Post 11/18 firmware update I'm getting 7.5-10 hrs. I run 50% brightness, adaptive brightness off, bluetooth off, Canary for my browser. Mostly reading in a MUI app, writing in Word, browser open with most extensions disabled except for AdBlock and Flash turned off.
As soon as I'm back on power and at a desk I turn bluetooth back on for my Arc Surface Mouse and re-enable my browser extensions.
Anybody else run Battery Bar, pro or otherwise? On my SP3s it jived very closely to what Windows power tells me. On the SP4 it's not even close or accurate. Windows always tells me I have way more power, time than Battery Bar Pro does.