See here for more help. At a minumum you can just snip off the legs to remove the battery if you don't want to dissasemble the motherboard, etc. Just carefully snip the legs off and clean with alcohol.
http://amiga.serveftp.net/hardware_repair.html
Ditto, But be careful not to damage any of the surrounding components while clipping. It doesn't look too bad and it aint going to get any worse in the next couple of days so there is no need for panic. Snipping the battery off at the legs is a good interim solution.
It is then easier to snip each remaining tabs in half so that you can un-solder each of the four solder points more easily and extract them one by one with small pointy nose plyers.
Use isopropyl alcohol and a fine bristle tooth brush to kill off those crystals..
You can do the initial clipping without removing the MB if you are looking for an interim solution.
