I use some vinegar + water to neatralize it and then use metho to clean the area, you can use a toothbrush to do this. Once the area is cleaned I dry the board with a hairdryer then spray some PCB lacquer after repairing it to protect and prevent further corrosion.
You can remove the battery by using some wire cutters. The proper way to do it is to unsolder it from underneath, you can also replace it from the top side of the board if you're really good with a soldering iron.
