What hardware issue can cause "Battery 2: Not present" in windows 10 (or Ubuntu)

So I have two identical tablets. Both have a docking station with keyboard, extra battery and extra HDD. (Medion Akoya S6214T for those interested). One of the two tablets does not detect the second battery (keyboard and HDD is detected) on both docking stations. I am sure it is the one tablet because the other tablet detects everything as should be. I am convinced it is a hardware issue because I installed Ubuntu live on both tablets and I get the same behavior (the one tablet fails to detect the second battery in the docking station). Funny thing is though: windows 10 displays both batteries

Question by BDesco on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.