I know this is 2 years late, but if someone else sees this then I hope it helps them.
When releasing the clips that hold the plastic back on you want to pry away from the screen and then kind of away from the device. It takes much less effort than you think if you are prying down and away.
Like I said I hope this helps. The rest of the guide is spot on. Have a metal spudger for the adhesive that is keeping the battery stuck to the device.