Split from this thread.
I am seeing the same issues on my Surface Pro 4. I used to get 4-5 hours per charge, now I am lucky to get 1 or 2. Everything was fine before the latest round of August Windows+firmware updates.
It dropped from 92% to 49% just doing some browsing for 30 minutes looking about this problem, on "recommended" power state, after a full charge and a restart. :(
Here is the report: https://1drv.ms/u/s!Ai_y9q83q0xWuEpzVc19MT50r70R