battery acid has damaged my devices

"And to make things worse, the same has happened with my wireless keyboard and the battery that's in deepest is stuck and I haven't found any kind of tool that can pull it out."

A small, strong magnet glued on the end of a stick might do the trick. The battery should stick to the magnet, but the trackpad itself is made of aluminum, so will not attract the magnet.

For anyone else concerned about this happening, you might try using a long cotton swab to apply dielectric grease inside the battery compartment before putting batteries in.

Re: the wireless keyboard, I thought I had a battery stuck inside after removing 2 batteries because looking inside it resembles the end of a battery. Only after removing the grey cover in the center did I see that it's just the seat for the batteries.

I have the same problem with my trackpad as Rod does, doesn't work after removing corroded batteries and cleaning. Doesn't appear to be any way to get inside the switch end though that defies logic since they had to install the switch somehow.