06 525xi electrical short

My 06 525xi randomly acts like the battery is dead
but it’s not. I had it tested came back good. When I
try to start the car the dash lights flicker and if I
continuously hold the key over instead of one click
over to start it it will eventually start. However
several codes will come on and then go away after
driving. Yesterday I had to put a jump box to the
battery and do the same thing till it finally started.
What could be causing this