Use toothbrush and brush off the corrosion area. Look at the traces and make sure that they are not corroded through. Check any chips that maybe had some of the corrosion on the legs and make sure to brush it off too (sometimes leg on an chip can get connected by corrosion and cause the chip to short. Forget the battery its only used for time and date anyways. I have repaired A4000 MBs with really bad corrosive damage (3yrs stored after they stopped working). Use alcohol with q-tips a plenty to make sure it is cleaned to the t. Good luck
