on mine the batteries are connected by the trombetta,controlled by the bird or the emergency switch. I had a similar problem and found the trombetta was sticking. replaced it for about 40 bucks on amazon.in simple terms if anything is charging any battery the trombetta connects all batteries so they all charge. if one shows a discharge it separates the coach batts from the chassis batts so you don't kill all batts. when you press the e-switch and hear the click that's the trombetta connecting the batts.just because you hear the click tho does not mean its working properly.
__________________
|