Battery configurations... will this work?

[pimplepounder]

You can use your 38 amp alternator to charge all three but not at the same time. You will need a three position switch. Seeing that your trolling motor will use two 12 volt batteries in series you can charge each of them individually with a 12 volt AC generator (Technical name for alternator) . The best method is the slow charge rate from an ac charger that you plug in, but using an inverter would require that the engine runs a long time to replace the charge and it is much less efficient so it would take even longer and require fuel. I am assuming that the 7 amp charging system is from the stator system on a kicker motor? This would be adequate to keep that battery charged and possibly your main battery, but it will work its tail off.

You need to be aware that connecting many systems together can bring about problem that result from electrolysis.( the transformation of metallic compounds resulting from current flow) All of the systems and batteries need to have separate conductors paths and never use the hull, stringers, or chassis as a ground path. It can literally eat away your boat, and outboards/units

My 2 cents

Kent