I suspect that the other posters may be correct, but if you're going to try to fix it...
Rinse the board with a weak vinegar (use white vinegar) solution or similar. The battery leakage, in this case, is a base, not an acid, IIRC. Ah, just did a search, and it is indeed a base. This link may have useful PCB repair information: http://forums.arcade-museum.com/forumdisplay.php?f=14
This is the one confirming alkali/base batteries: http://forums.arcade-museum.com/showthread.php?t=117707
Fortunately, the region of the board which was exposed seems to have a lot of blank or filled areas and not too many vias (holes connecting one layer of the board to another layer of the board). Also, it looks like the solder mask (green stuff) protected the board for the most part. The only areas likely to be damaged are exposed copper and solder at the pins of chips and in vias.
Unfortunately, there may be some of these under the chips as well as the ones that are visible.
While the chips look bad, the damage should be only on the package/pins, and not the internal silicon. So as long as you can clean up the pins and don't break any off, the chips may be recoverable.
That sound chip looks like it needs to have all of its pins cleaned and resoldered. There's at least one other in those pictures that also needs that. You probably need to remove the chips and check the pads underneath to see if there's anything left of them. Also to check for any vias which may be under the chip.
Use a heat gun or hot air gun to remove the chip and be really really gentle with it. Use plenty of flux on the solder joints before desoldering. Also, you may wish to cover any surrounding small components (SM resistors or caps) with modeling clay so that you do not accidentally desolder them.
When you desolder those components, don't apply any force lifting the chip. Make sure all the solder is fully melted first. You must be extremely gentle in this case to avoid tearing or lifting pads (or what's left of them).
Check the continuity of all of the traces connected by vias. The vias which connect to capacitors probably go to the ground or power planes, so you can check their continuity to any 5V or GND connection.
The battery holders are still available. I know DigiKey sells them. There is probably a European supplier.
Rinse the board with a weak vinegar (use white vinegar) solution or similar. The battery leakage, in this case, is a base, not an acid, IIRC. Ah, just did a search, and it is indeed a base. This link may have useful PCB repair information: http://forums.arcade-museum.com/forumdisplay.php?f=14
This is the one confirming alkali/base batteries: http://forums.arcade-museum.com/showthread.php?t=117707
Fortunately, the region of the board which was exposed seems to have a lot of blank or filled areas and not too many vias (holes connecting one layer of the board to another layer of the board). Also, it looks like the solder mask (green stuff) protected the board for the most part. The only areas likely to be damaged are exposed copper and solder at the pins of chips and in vias.
Unfortunately, there may be some of these under the chips as well as the ones that are visible.
While the chips look bad, the damage should be only on the package/pins, and not the internal silicon. So as long as you can clean up the pins and don't break any off, the chips may be recoverable.
That sound chip looks like it needs to have all of its pins cleaned and resoldered. There's at least one other in those pictures that also needs that. You probably need to remove the chips and check the pads underneath to see if there's anything left of them. Also to check for any vias which may be under the chip.
Use a heat gun or hot air gun to remove the chip and be really really gentle with it. Use plenty of flux on the solder joints before desoldering. Also, you may wish to cover any surrounding small components (SM resistors or caps) with modeling clay so that you do not accidentally desolder them.
When you desolder those components, don't apply any force lifting the chip. Make sure all the solder is fully melted first. You must be extremely gentle in this case to avoid tearing or lifting pads (or what's left of them).
Check the continuity of all of the traces connected by vias. The vias which connect to capacitors probably go to the ground or power planes, so you can check their continuity to any 5V or GND connection.
The battery holders are still available. I know DigiKey sells them. There is probably a European supplier.