Looking at getting an extended battery for my S4. Yes, I could go with an extra OEM battery, but if my experience with the Bionic is similar, the S4 will probably feel better in hand with a little thickness.
Just wanted to toss it out to the community to see if anyone has had any experience with the Anker (5200mAh), Hyperion (5200mAh), or Mugen Power (5500mAh). All are NFC capable. Through Amazon they're all less expensive options than a Mophie or Incipio battery case, and they don't increase the overall length.