I was recently experiencing that my macbook pro was losing its battery, even when the lid was down.
I would simply close the lid of my macbook pro when i go to sleep at night. However, it would end up being totally out of charge by the time i wake up!
Why did macbook pro drains battery even when in sleep mode?
The macbook pro had bluetooth turned on. Well that itself is not at all an issue with battery, but in settings, there is an option that was an issue.
How to fix the macbook battery draining even on lid down
To solve this issue, go to: system preferences > bluetooth > advanced
And uncheck (disable) the option for:
Allow Bluetooth devices to wake this computer
Click ok and you’re done! Now your battery won’t drain even if you put your macbook to sleep by putting down the lid, even with bluetooth turned on or even connected to a device like bluetooth headphones.