Can keeping my MacBook Air in sleep mode or with lid closed for 3 days drain battery?

Hi,

I searched "battery life" before I came here to ask, but most were about the iPhone batteries.

So I think my battery was at 50% when I last used it and thought I shut it off; guess I never did. Then I got busy working etc and didn't even use my MacBook for a few days. So now I opened it expecting it to turn on and it never did, Plugged it in, and it's red at only 3%. Can keeping it in sleep mode or having the lid closed for 3 days really drain the battery? thanks

[Re-Titled by Moderator]

Original Title: Battery life? - left on for days with lid closed