How can I know if the Samsung battery I bought online is original?

Ways to Know Original Samsung Battery

1) Battery Label Design of Samsung Original Batteries 

  : Next images shows the layout of how a typical Samsung Original Battery label should  appear. 

(Overview of Certification Mark (Certi. Mark) , Warning Design , Serial Number(S/N)

2) Different Warning Design by device types of Samsung Original Batteries

From next images, we’ve specially focused on comparison between Galaxy S5 Original and Fake devices.

3) Label 

    : Label texts and warning icons are different from original.

4) Battery contact 

   : The battery contacts should appear “recessed” and not protrude from the battery case.

5) Battery appearance 

  * In this example, we used a Non original battery for GT-I9100 device compared against Samsung original. 

Source: Samsung Website!