I've fixed this before. My wife took the keyboard to an Apple store and they had no solutions. I told her to put it in the freezer after sealing it in a zip-loc bag. Left it over night. Opened the battery cover and lightly tapped the keyboard, batteries slide right out. Ours were not corroded but the Applet told my wife that this was an issue with this design and that the batteries swell. Swelling? How about ice. I wasn't sure it would work thinking that the keyboard battery chamber may shrink a bit as well. If it did it was insignficant relative to the shrinkage of the batteries.