T&T: Battery for MDJF Gen Set

[Bob]

Onan Training Manual (Table on Page 20) says my 15.0 MDJF-3CR/2268C, Serial
Number 0572438196 requires 2 each 6 volt 5D batteries CCA 800, Approx  Amp Hr
(kC) 190(684) Onan Part No. 416-0437.

However, I have been using (came installed in the boat from previous owner) a
12 volt Yuasa GSGT-130F51 battery which is now dead and needs replacement.
I'm wondering if this is the wrong battery as the training manual says 6 volts
instead of 12 volts?  I would like to clarify this before I purchase a new
battery for this Gen Set.  I would like to know what type of battery is most
suitable for this Gen Set?

If two 6 volt batteries are recommended as specified in the Training Manual
(old manual), should they be connected to produce 12 volts or 6 volts?  I can
not find any explanation on this in my Owner's Manual, Training Manual, etc.

I have Faxed my local Onan Dealer here in Japan and will post their response
on the list once I get it.  In the meantime would like to hear from others on
the list who have a similar generator and what battery you are using for it...
details... voltage, amps, cca, etc. would be appreciated.

Thanks.