I have a diesel van that has a dual battery starting system. Each battery has 850CCA. I have 75w of roof mounted solar panels that are running through a 100amp controller and charging an aux battery that has 55amp hours. All batteries are 12v. I would like to be able to charge my aux battery when the vehicle is running without drawing down my starting batteries when the vehicle is not running. I do know the difference between series and parallel. I will be wiring 12v parallel. Several questions: Can I use a simple disconnect switch instead of a controller or do I need to have a controller becuase the aux is smaller and less amps than the starting batteries? (still 12v) Can I run the positive for the aux battery through a controller or switch to the closest positive terminal on the #2 starting battery (which is about 10ft closer than the other stARTING battery) or do I have to run it up to the alternator? With this setup can I just connect the aux negative to the frame or does it have to connect to the charging battery? I don't see why I couldn't just tie into the closest battery and use an isolator in between but the RV dealer and my personal mechanic are telling me I have two run all my wiring all the way back up to the front of the vehicle to the alternator. There is about a 10ft differece and a real pain compared to jumping to the battery that is 2ft away. But I am not sure if it will damage the system in some way... If it will improperly drain the one starting battery and cause some sort of charge loop problem. Also, I am concerned that the aux battery will get damaged becuase it is not the same amp rating as the starting battery... does it make a difference? Since I have the solar panels on its own controller will it damage the panels when charging from the alternator? I don't thing it would but am not sure.