The battery was really glued down tight, and pulling the plastic tab eventually ripped the tab off and I could no longer use it. After 15 minutes of gently lifting with the plastic opening tool and getting nowhere, I followed the suggestion about using a hair dryer to soften the glue. I blew heat on the back of the phone where the battery is for about 30 seconds, and then used the plastic tool on the side of the phone with the volume buttons, and it lifted out with very little resistance.

I want to stress that it was not a ton of heat--I held the phone in my hand while using the hair dryer, and it was hot on my hand but never so hot that it burned me. The point isn't to cook the phone, just to warm up the glue so it gives a little.

Prying from the volume side will also reduce the chance that you dislodge the GPS connector.