I will see if I can explain better. I only have one battery for the truck camper and it sits outside the camper by the wheel well.The only way it is charged is from the 7 pin plug from the truck to the TC and the on board converter.I am thinking the battery should be grounded so that the TC is also grounded. The reason I ask is what do people have when the batteries are inside the TC how is the system grounded. Thanks, when it comes to battery tech the people on here are very smart.