Is the iFixit replacement battery genuine?

I plan on picking up a used iPhone 5S. My only concern is the remaining life left in its battery. My plan was to just bring to Apple and pay for their obnoxious $80 replacement battery service. With this, I'd have the piece of mind that the battery being installed is a genuine Apple product and guaranteed to be "new."

or

I could just buy the replacement battery kit from iFixit. However, are these batteries genuine and/or trustworthy? Also, am I guaranteed that the iFixit battery will be brand new? And I mean brand new/unused/non-refurbished/etc.. I understand that everything is tested, but charge cycles should be less than 10 (even less than 5).