if you are going with 12v batteries you wire in parallel. (parallel keeps voltage the same and doubles AH). if you are going with 6v batteries you wire them in series (series doubles voltage and AH stays same).<br><br>for best performance and the least amount of goofing around, buy the same type, size, AH and even brand. when you purchase, check the manufacture date label. get the newest one.<br><br>when you add batteries to your existing battery/bank, make sure that the existing battery/bank is fully charged and make sure the new battery is fully charged before hooking everything together.<br><br>age is not as important really as much as how your existing batteries were treated, charge condition, environment condition, depth of discharge and number of cycles play a role.<br><br>my current battery is a 4D 12v 200AH that has been well cared for. i intended to get a second with a few months but i have not done so. its been two years. a call to the manufacturer and the technician where i purchased assured me that adding a second or more, in my case and with their brand, should not be an issue even after two years. reason being is my battery was well cared for in a "known manner". they would not recommend it normally but feel as though im ok to go.<br><br>if you are talking about a delay of weeks or months then you should have nothing to worry about.<br><br>if you have the budget now, get all 3 or 4, with the same date code, and dont give it a second thought.
