Shai,

Now available in the Avsim library, search for:   cs737_apu_gen_grdpwr_mod.zip.

This did it for me. Never had battery drain issues since. Can run just ground power for hours if need be and no drain.

Be sure and install Paul's V-one gauge, Bud's FDE tweaks,  and Dutch's engine performance patch. Without these, it's far removed from RW performance. With them, it's much more realistic and enjoyable.

Sorry you paid full freight ($54) for this AC with these and many more fundamental issues that based on history and track record, will never be fixed.