About temps: An Exide rep once told me that summer was the most lucrative in the battery business and that is in MN. I worked with a gentleman from Guyana for a bit and while talking equipment, he told me that the battery in a tractor lasted less than a year and they discarded them after that. It leads me to believe that batteries in hot climates have a toll taken on them thats above those in moderate climes.
I have split banks, too (AGM and 6V pair), and noticed the Morningstar MPPT controller has lowered voltages, recently, from Winter storage levels. I'll have to get out there with a laptop and see what is happening, now, throughout the day in warmer weather.