I think you have a total of 700AH @ 12V (6 x 700AH @ 2 volts = 700AH @ 12 volts).
If they really are gels instead of AGM's, you've gotta be careful to charge them properly. Gels can be ruined by overcharging or using too high a voltage.
This means you MUST have a regulator
which can be set for the type of batteries you have.
I assume your alternators will take an external regulator
, or can be converted to do so. If so, then you might use something like the new Balmar
MC-612H regulator which can handle two alternators charging
the same battery bank. And, it is fully programmable for the type of battery, various charging
parameters, % of alternator output to be used, etc. It also accepts sensors for battery temperature and alternator temperature.
First thing is to verify that you really do have gels, not AGMs, since their charging regimes are very different.