How to tell the difference between the old and the new battery?

I received a new battery and a new back case in the mail from ifixit.com and swapped out the old battery with the new one and replaced the back case without a problem. However, as I had to take out the battery several times to reseat it correctly, I may have grabbed the old one and re-installed it in error. I checked the charge on both and one is 55% the other is 62%.

I want to be certain that I did not reinstall the old battery back into the phone in error. Is there a way to tell the old battery from the new one?

The battery I presently have installed has a date ?/?/2017; the one that I took out and have on the table has no date.