There are two types of different adhesives holding in the battery that I have encountered. One is double-sided foam tape (easy to remove). The other is some kind of self-amalgamating tape (hard to remove). Please be VERY cautious when removing the battery.

I recommend heating the front side of the screen prior to completing this step (the battery tape is fixed behind the back of the screen).

The adhesive holding down the battery is located close to the side where the antennas are located (right side when looking down). To remove the battery, heat up the battery with a hair-dryer, then gently pull up away from the phone on the opposite site (left side).

NOTE: Be gentle with the small metal tabs on the edge of the battery; these are quite flimsy and will bend if used to force the battery. I removed the double sided tape completely here too, and did not replace it.