Scenario: A parked vehicle has a dual battery system with it's aux battery feeding the trailer fuse block (via 7 pin socket), and the trailer has a battery of it's own, wired in parallel, and feeding the same fuse block: a) Does the usage of trailer accessories draw from the aux battery of the vehicle, the trailer battery, or both simultaneously? How do the two batteries and their voltages and the load interact? b) Would a solar panel/controller that's connected to the trailer battery charge only the trailer battery and detect when it is fully charged and shut off supply to prevent overcharging (thereby not charging the vehicle aux battery), or charge the trailer battery first and then float charge the vehicle aux battery, or try to charge both batteries simultaneously? In other words, how would it behave? Trying to plan out my setup and this has me a bit confused. Thanks in advance!