Rewolf, you can fix your APX6 guitar preamp.
I've made a preamp repair guide, you can download it in pdf format from here:
https://drive.google.com/open?id=0B-8-tjpvVqN-NG9MNEFMOWVoRzA
here is a photo of part of the guide:
You have to take the preamp out and solder a new battery connector.
You can buy the battery connector here:
https://www.banzaimusic.com/Battery-Snap-I-IND-FULL.html
While you are doing this is should also do a revision on the APX6 preamp,
you can download the guide in pdf format from here:
https://drive.google.com/open?id=0B-8-tjpvVqN-NG9MNEFMOWVoRzA