After the original battery of my MacBook swelled up so much that it pressed against the touch pad from the inside and made the mouse move on its own and even produce clicks I didn’t intend, I bought a battery and tool kit and swapped it out. Apparently one has to be super careful that the provided glue solvent doesn’t touch anything else in the MacBook but the old battery. But so far I think I managed to do it! Yay!
This is how buying €100,– worth of spare parts saved me from buying a new €3.000,– Laptop.