Do I understand the question correctly, why the battery continues to discharge, if after 10 minutes without charge the avionics is disconnected from the battery network? Secondly, is this also the case when the APU is started and charges the electrical system? The former case I can not understand, because with me after 10 minutes nothing shuts off (FSX). The battery is able to supply the relevant parts in the electrical system alone for about 30 minutes, which is also implemented in the FSX, that is, now 99% of the displays turn off. In the second case you write the APU is running and all generators are on. The APU has only one generator, so are we talking about this one? So if you have a problem, please check to see if all required switches are correct, or put a picture of your problem.