2019 MacBook Air still sucks down battery when sleep
A while back Apple introduced something called "Power Nap."

Basically your Mac will still do some background tasks while asleep. I am guessing that this might be what is going on.

Go to 

System Preferences &gt; Energy Saver

and look for "Enable Power Nap while on battery power."

I would guess that it is checked, un-check it and see if that helps. 

Also there is a good shareware app out there called Coconut Battery that will give you some detailed info on battery health and usage, you may want to look into that as well.