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Alex,
the current rating on any MPPT regulator determines its power handling capability, that’s why an MPPT regulator with say a 60amp rating can handle 720 watts at 12V (actually a little over that as the battery voltage is around 13.8 at float) but at 48V is capable of handling almost 3KW. Of course you need the panels to drive that power. There is a 2 fold advantage in going to higher voltage battery banks, the first is that smaller size wiring can be used, the other is that MPPT regulators can handle more power as the voltage is increased.
I’m not sure how Greg came to the conclusion that SLA or AGM batteries are flat at 50% discharge, that’s simply not the case, you can discharge lead acid type batteries deeply but there is a penalty, the deeper the discharge the less cycles you will get from the battery before it fails. Keep the discharge to 20% or less of the capacity and your batteries will last, I have batteries at my shack that are over 10 years old and still going strong, my setup is sized so that daily discharge is 20% or less and my solar array is oversized so that performance on less than ideal days is adequate.
Also returning Lead acid batteries to a fully charged state immediately after discharge is critical, the longer they are left in an discharged state the harder it becomes to reverse the sulphation that occurs during discharge.
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