Finally! Thanks everybody. I started yesterday and got one battery out by hitting the side of the key board. Then went to two Mac stores, and one owner got one more battery out by poking and hitting, but the third battery was stuck. All batteries were swollen with corrosion. Today I tried a little moist baking soda, before went on this site. Then, as suggested, I tried a few drops of vinegar, twice, finally, I went to WD-40 and waited a few minutes, hit the board more on the side. Nothing happened, so I gave it another shot
of WD-40, and poked the battery with the long screwdriver. Battery didn't move, so I just slammed it down really hard flat on the back and out popped battery #3. So I cleaned it up with soft rag and screwdriver - don't know yet if it still works after all that hitting and slamming.
I new would have got this far without the above postings. I should know better than to leave anything electronic for a long period with the batteries in it.