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Hi wet cell man - as a fella thats been, in the past, entirely dependant on batteries for all lighting and power in remote areas (mainly wind, some solar) I'll depart from my normal stirring, flippant thread-posting nature and give you my (educated and experienced) 2 bob's worth!
First of all I'll presume you meant 700 Ah capacities triple cell batteries (bloody small subs if they're operating from 70AH units!) - but having been unable to avoid that comment I can state categorically that there is no problem/danger in paralleling up 2 sets to create (nominally) a 12 volt 1400Ah system - though if they are indeed 70Ah units series configuring them into 2 banks of 12 volt 70Ah units will only give you 140Ah capacity.
When you parallel batteries (which are, technically, a series of individual 2 volt cells) you effectively double the capacity - presuming the two sets are of equal "storage capacity." If they aren't, you'd run into problems like discharge between the "pairs" but if they are all the same types that is not a problem. Series connections raise the output voltage (ie two 6 volt units where the negative of one unit is joined to the positive of the other and the resultant "unjoined" terminals become the composite unit's neg. and pos.) but the storage capacity (Ah) remains the same as one individual unit.
Those types of batteries (rather the individual cells) are usually rated at what they call the "10 hour rate" - meaning that if they are 700Ah jobs they (technically) should deliver 70amps for 10 hours without significant drop in output voltage. (I have, in another life, tested hundreds of similar cells used in remote area exchanges for what was PMG/Telecom/Telstra.)
This current (70amps) should also be the maximum charging rate, and to ensure the longest life from the batteries they should be kept at or near fully charged permanently - this is known as "floating" the batteries.
Trickle-charging them once fully charged is the go here: and whilst, as someone has already commented, some recommend "gassing" the cells occasionally, this is not really advantageous except if the batteries have been allowed to run down and have sat discharged or semi-discharged for some length of time and become somewhat "sulphated". This is because this sort of treatment (giving them a boost when they are fully-charged), promotes plate disintergration and even though these types of batteries have a large capacity for charge and a large "collection" area at their bottoms to store disintergrating plate material it is unhealthy for the batteries.
If the battery charger you are using is a decent one (well regulated) then if the trickle charge is around a maxmum of 2 to 3 amps when full charge is reached it can be left on continuously without overcharging the setup - but as someone has already stated, a hydrometer is essential to keep the electrolyte at around SG 1250 (actually 1.25 but written as "1250" and remember to maintain the level up to the top marker Some applications advise 1260 SG - but not for these units and your proposed application. Naturally electrolyte level is maintained with distilled water.
As for placing them: a good pallet (or two) makes a great support on a conc. floor in a well ventilated room/shed - and finally, if they are the clear plastic type cells, I should add, faced with a cracked and leaking cell that needed emergency aid once, I found that "Plastibond" was the only material to effect a repair without draining the electrolyte - which you can't do, because the plates will heat up, "steam" and self destruct!
Regards, Kokatha man.
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