Bev/Chas,

• theoretically, could you create a bank that had 2, or 4, flooded 6 volts,
  connected in series, and also attach a 12v flooded starting battery?

Depends on what you mean by "attach."  Yes, you can parallel a single 12V battery into a 12V bank made up of pairs of 6V cells in series.  The internal electrical characteristics of these two arrangements - even if all are flooded wet cells - would be slightly different due to battery capacity, construction and aging differences.  So, both charge and discharge current flow balance would be different within them.  Wired together, the terminal voltage of the bank would be held at the same level, but circulating currents would flow and cause unbalanced loading across the different construction batteries.  These effects are less if the batteries are of the same type, but not zero, and probably not negligible.  All of this would certainly be OK if switching them together on an emergency basis.  "Emergency" here means short duration, as to start an engine, but not longer duration, as to supplement bank capacity for running inverter/charger loads all evening every evening.

• we will move our 8D AGM's to 6 volt golf cart batteries and also have a
  smaller AGM starter for our genset. Should we leave it as an AGM to be
  charged like a flooded or change that one out also? It's only 1 year old.

So what you're saying is that the house bank and genset start battery would be paralleled and charged from a common charging source, right?  If you only have a single charging source, I would only parallel in the genset battery with an automatic charging relay (solenoid), not a manual paralleling switch, and definitely not permanently wired in parallel.  This is about not accidentally discharging the genset start battery with house loads, and then, as a consequence, not being able to start the genset to recharge the house.

Ten years ago, before 3-stage chargers had separate charging profiles for AGMs, several manufacturers recommended using the flooded wet cell profile for AGMs.  Today, not so much.  The charging profiles for AGMs and flooded wet cells are very similar, but not identical.  Another catch is, the genset itself will probably charge it's own start battery.  It'll probably do that like an automotive start battery, at a constant 14.6V, which arguably is worse for the AGM than 3-stage charging with a slightly off flooded wet cell program.  Since it's relatively new, I'd go ahead and use it.  You've already paid for it, and you might as well get the capacity it can return over its service life.  Start service is much easier on the battery than deep cycle service, and use is less consistent.  Swap it out to flooded wet cell when it gets to end-of-life.

Hope this is useful.

Jim

Peg and Jim Healy aboard Sanctuary, currently at Charlotte Harbor, Punta Gorda, FL
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Jim,

I completely agree with you regarding use of flooded 6V golf cart
batteries for house bank and engine starting.

However, I feel that use of a non-flooded VRLA battery for the generator
starting battery is best.  I've used a GEL battery on my generator for
the last twelve years.  (The same one in fact, its never needed
replacement).  The reason is that I feel that the generator battery
shouldn't be connected to a charger on a regular basis.  Its only use is
for a few seconds in starting the genny. The generator charging circuit
should maintain the charge on the battery.  Plus, VRLAs have much lower
self discharge than do floodeds.  So there is not the need to constantly
maintain them with a charger.  And keep in mind that more batteries are
damaged due to mischarging than die of old age.

One of the problems that arises by not maintaining a battery on constant
float charge is the potential for sulfation of the plates that occurs
when the batteries SOC falls to less than about 80% due to self
discharge or otherwise.  Whereas VRLAs have smaller self discharge and
they are less susceptible to sulfation, they can be left off of charge
without the type of difficulties that would be experienced with
floodeds.  I will add that GELs do have the lowest self discharge and
are less susceptible to sulfation than AGMs - thus my choice of GEL.
But if an AGM is already in place, then I see no reason to replace it
early.  Possibly just connect it to the charger through a switch for a
few hours once a month if the generator is not being used on a regular
basis.

A means of paralleling the generator battery in the event of an
emergency would be advisable.  But otherwise, the generator battery
should be connected only to the generator.  As far as the generator
charging characteristics not exactly matching the VRLA battery, this
might be a problem if the generator were run on a 24/7 basis, but for a
generator used only a few hours a day, it likely won't be a problem.

Tom Collins - Misty Sea