I share Harry's opinion. You can get by with replacing only one battery but that just sets you up for trouble later on when the older battery decides to cause trouble. Since you have two batteries in parallel, trouble on one battery means trouble on both batteries. The good battery could discharge into the battery with bad cells. It's just not worth the hassle that will happen later.
About 4x6V batteries - it's all about ampere-hour capacity. The 6v batteries probably will have more capacity that the 12v, but you need to look at the battery specifications. When you do the math, remember it takes two 6v batteries to make 12 volts so you only count the ampere-hours of one 6v battery when adding up the capacity. For example, assume each 6v battery had 200 ampere-hour capacity. The total ampere-hour of a bank of 4 batteries would be 2*(200) or 400 ampere-hours.
__________________
--John
2005 Horizon 40AD, 2005 Jeep Liberty CRD
|