Best way to combine Mains and Solar charging ?

[affinite]

Would a Battery to Battery charger help the original poster? I understand they take the full current from the engine alternator (if needed), even when engine speed means that the Alt is not running at maximum output . I assume the BB charger overrides the Alt regulator to achieve this?

I already have a Sterling A-B charger fitted.
I think it's designed to do what you describe but I'm not sure its working properly as I don't remember seeing charging current anywhere near what I expected .
Its top of my list of things to check when I can get to the boat