Join Date: Jun 2013
Location: Central West NSW, Australia
You would need to do it like the 4x4 and caravan guys do it. They put a switch in the system that isolates the second battery when the motor isn't running so that you can drain the aux battery without leaving yourself stranded, but also restrict the charging current to it so that the inrush into a dead battery doesn't overload the charging system. The electrics in these bikes are not overly sophisticated, and for normal bike use they don't need to be. That doesn't mean it's impossible, but it's a lot more expensive than just hooking a second battery up in parallel with the normal one.
You might be able to get a small charger than plugs into an aux socket, which would be the easiest solution that doesn't cause substantial fire risk.
"I've recently come to the realization that true happiness can often be found at the bottom of an empty gas tank" - Prime