Hello,

We've seen this chain before, but there are so many new folks these days, 
perhaps a couple of things need to be said.

1) Which is better?  I think that no on knows for sure.

2) The diodes.  Yes, there is a 0.6 volt drop.  However, if the
   voltage sensor of the regulator is on the battery side of the
   isolator, the batteries will be charged to capacity, and at the
   about the same rate as without the diodes.

   The problem is that the voltage sensor can be connected to just
   one of the batteries.  Which should it be connected to?

3) The relay.  What happens when a discharged battery is connected
   across a fully charged battery?  Even if bad things don't happen
   because of high currents, the charged battery will lose at least
   some of its charge to the discharged battery.

I'd say both systems work just fine, but both have side effects.  Both have 
been around a long time and both are used in commercial as well as RV 
applications.

Take your choice.

Mike  (Qualifications: ancient EE degree)