Batteries not charging while chassis engine running

Do you have an auxiliary start switch on the dashboard? Flip/press that switch, do you hear a click from the solenoid in the battery box? If so, you probably have the same problem I had, the contacts on the solenoid have so much carbon buildup that it won't allow current to pass through. Simple fix, I bought the generic 3 pole solenoid off of Amazon, $15 & 15 minutes to replace!