Any idea what happened to my battery?

[Andysapple]

So I took my MacBook with me to school at 8, but didn't use it. I came home after 12 and plugged it in for a few minutes (to power and my external monitor) before taking it out again and brought to my couch. I noticed after a few minutes that my battery had went down 14 %. Any idea what happened? Is this some battery saving feature or is something wrong with the battery?

 

[SquealingCustard]

Do you have any antivirus installed?

 

[Andysapple]

Nope!

 

[SquealingCustard]

Hope you find your answers and to put it into perspective I used my MacBook Pro from 9am to 11pm Saturday and then 9am to 10pm the following day on battery and it only dropped to about 55%