I went up in January to do battery maintenance at the cabin. I found that the first battery in the string is failing. I think I will try to replace just this single battery for now. I know that's not the preferred path to take, but we are saving for a new set of Lithium batteries to replace our 8 year old lead acid battery bank. So we'll see if a single replacement will give us some improvement. This picture shows the battery voltages for each of the 8 6-volt batteries. The top number in each figure is the voltage after a full charge cycle, and the figure at the bottom is the voltage after a discharge that brought the bank below the low voltage threshold. Notice on the upper right hand battery that the voltages are significantly lower than the other seven batteries. That is the battery that needs replaced.