I had my bank split into two strings for a few months this past fall. And when I attempted to go back to series/parallel, I found I had to get the two strings to a very similar resting voltage, before they would play well with each other. For example, the two strings would continue to maintain different resting voltages, and the string with the higher voltage tended to hog most of the charge. It was worse, the further apart they were in resting voltage. And I'm talking only about .03v difference. Now they're sitting dead even, throughout.