I live in Nicaragua.  I purchased 3 banks of 4 Outback 106NC batteries two years ago.  They have done well, but now one of the twelve seems weak, I first noticed this when battery performance fell around the end of October, and quickly discovered the problem.  While all the batteries charge equally, and perform equally during the day (even if the solar panels are disconnected and a 1.5 kW load is used, they hold up equally well), and work equally for a few hours into the evening, after that one of the batteries starts getting weak much faster - after about 1-1.5 kWh of use.  By morning, if I let it run that way, there is a 0.8 V difference with the other three batteries in the string without a load, and 1.4 or more with any sort of load.  At first I just used the batteries mostly as a backup at night while I tried to resolve this (I do have the grid), and then I disconnected the string with the bad battery and started just using the two.  The string with the bad battery was fully charged when I disconnected it, and all four batteries have held their charge about the same for over 48 hours, going down to 12.7-12.8 V.  I contacted Outback and they told me not to run the string with much charge difference, which I had already guessed, and recommended a few things to try, like increasing the Absorb time, which didn't help.  They told me that the 106 NC has been discontinued, and they could not tell me what other battery if any would work.  They gave me a phone number for the actual manufacturer, who then referred me to one of their engineers, but that fellow does not answer his phone or return calls.  I need to figure out what to do, and whether I need to buy all new batteries in a case like this, or if there is some sort of reconstruction that could be attempted, or whether there is some other battery I can put in the string.  Any ideas?