My wife has the same laptop and the fix was to adjust the pmset settings. It would lose over 15% overnight. There are different modes of "sleep". I will call the first "instant wake sleep" and the other "standby sleep."
Go into terminal and input "pmset -g"
See what your standbydelaylow and standbydelayhigh are. These values are the time in seconds where it waits until to put your laptop into standby mode, which consumes way less energy if there is not an issue with wakes.
I found the default was 24hours. I have changed these values to 3600 (1hr). Now we only lose 2-3% overnight. It will slow wake up time to about 4 seconds instead of instant wake but well worth it.
As stated earlier this works for us but you suspect wake issues, but modifying these values should be done to your preference.
If you want some good reading, type "man pmset" in your terminal. It may have some settings in there that make help on wakes.
