As well as this i've also got a solder sucker thing which should be useful for pulling away the molten stuff.
Personally I'd recomend you go to a electronics shop and ask for a wick. Let the soldering iron heat up, put the wic on top of what you want removed, and place the tip of the soldering iron on the wic. Watch the wic closely and you will see when the solder melts and gets sucked into the wick. Do this a few times for each post, moving futher down the wick. You'll get to a point where the battery is probably still stuck in place but most of the solder is gone. Then put the iron right on one post at a time while tuging lightly on the battery. You will feel the post come out. Once the battery is completely out use the wick once again to get any left over solder off.
