I have read that it is better to have two 6 volt batteries in parallel rather than one 12 volt,
Two 6V batteries in PARALLEL make a 6V bank. Two 6V batteries in SERIES makes a 12V bank..
but at twice the cost is the benefit twice as much.
Actually $$$ to Ah's 6V batteries are less costly. The typical GC2 6V golf cart batteries will yield about 225 - 240 Ah's and almost always for less money than 12V batteries. To equal that capacity in 12V would run you more $ for two 12V batts and take up a larger footprint.
Here's an example from the same retailer:
12V Deep Cycle 75Ah = $69.76 X 2 = 150Ah's = $139.52 = 93˘ Ah
12V Dep Cycle 90Ah = $77.76 X 2 = 180Ah's = $155.52 = 86˘ Ah
12V Deep Cycle 105Ah = $84.67 X 2 = 210Ah's = $169.34= 81˘ Ah
Deep Cycle 215Ah = $78.83 X 2 = 215Ah's = $157.66 = 73˘ Ah
6V Deep Cycle 230Ah = $88.74 X 2 = 230Ah's / $177.48 / 77˘Ah
At about the same cost you could have two 12 volt batteries and would that be better that two 6 volt??
No, it would not be better in terms of either cost or longevity.. One thing the above cost example leaves out is that 6V golf cart batteries will survive many, many, many more "cycles" than a deep cycle 12V battery. Trojan for example says up to 50% more cycles that their 12V brethren. So not only are they cheaper on a $$ to Ah scale but they will also outlast a 12V battery too making the $$ to Ah conversion but a small piece of the cost analysis....
I am talking about deep cycle for house bank needs, I have 4 golf cart batteries now and cruise every weekend and in the marina it is on charger. I also have twin solar panels and a wind charger. Plan next year to cruise and anchor out a week or two at a time.
Any suggestions on which way is better?? Also have separate starting bank. Thanks for any help.
Stick with what you have. You have a series parallel bank that will outlast just about any12V configuration that would fit in that foot print and you have it for less money..