If your MacBook is working with the charger, then you may as well use that so you have a working computer.
Since you had an unauthorized service replace the keyboard and trakpad Apple is not likely to do anything more to help, they are very emphatic about not providing further support to a machine that has been worked on by an unauthorized repair person. You can take it to an Apple store genius bar and see what they say and if they will help.
The Retina is pretty much a single unit internally. The ram and solid-state storage are soldered to the logic board. The battery can be replaced, but the replacements are difficult to get since they are an Apple proprietary design. Iff you can take the Retina to an Apple store, either in Europe or back in the US, try and see if they will help you. There is nothing more you can do at this point as parts are not readily available to you.