JD , This has been discussed many times and I have put the picture below to show my arrangement with 12 batteries. As you can see the front row is a mixed row where one went bad amongst some 4 year old ones and was replaced with one three years old which would have similar characteristics to the rest in that bank. The new ones were at the back ( Exide G90) and not connected directly to the feed cables from the invertor but off set by one link. The middle row where also old so the direct feed went to them. That was the arrangement at July 2013 so about 20 months ago. This only applies to Flooded Lead Acid Batteries and I dont think it applies to Gel Types
The front row was replaced by a new set in August 2013 with US 245 Diamonf plate technology Batteries for about RD$22,000 . The old ones were sold for RD$ 700 each. like this :
This photo was taken 22 Jan 2015 we are now going to replace the middle row with four new ones.!. The main feed will be moved to the back bank and the red ones move next to them , the new ones will go in the front and be two links away from the main feeds.
The point is to check you batteries with a load tester like this and ensure they all read "GOOD" before including them.
There is another side to this discussion. If one battery is bad as is often the case I have found that "Electricians" will recommend replacing all batteries since this is a safe and lucrative bet on their part. Four new batteries - RD$20000, fitting etc say Rd$3000 - everybody happy - you bet!! Electrician then sells the three "good " Batteries he has just taken out for RD$ 2000 each = RD$6000 , and the scrap battery for RD$700 - Not bad !!! Think what this would be with twelve.
Happy customer, RD$9700 for the job! Happy "Electrician" - an interesting "SCAM" !!!
Think about it !
Olly and the Team