Hello iw2fvo,

I have not really read the documentation I linked yet, (really just browsed it). You might be saying the same thing, but it is my understanding that MPPT senses battery voltage, calculates what charging voltage is required, based on that, converts PV voltage and current to match what the battery needs for charging. This would be the highest current available to charge the batteries.

For instance,
Assume your battery is low, at around 11.5 volts. A MPPT takes PV output at 16.9 volts at 7.1 amps and converts it, so that what the battery gets is no longer 7.1 amps at 12.5 volts, (which standard charge controllers will do) but 9.6 amps at about 12.5 volts using MPPT. If you bring the amps up higher, you drop the voltage, and if you drop the voltage much lower, you won't be able to have the current flow into the batteries.

Here is one last link that explains in very general terms how MPPT works. It is not great, but I have not found a better general explanation. http://www.solar-electric.com/charge_controls/mppt.htm