Battery Life

How can I know that my Macbook has an acceptable battery performance for its age ? I have the feeling the level is falling down very quickly. Im not charging it right now , brightness: 6blocks ; only safari open ; 3% consumed in 10 minutes? I have only 100gb of files on hard disk, mostly books. The only extra programs are SPSS statistics, Skype, Microsoft office, and WhatsApp. All other are standard apps. I have Mac OS High Sierra installed.