hmm, Im not sure I follow your logic on amps.
You are right, if it is only 12.7 volts then that will not matter if the solar is charging at 14.
This is 1970's technology, 15 amps is a decent amount of power to flow continuously. I don't think the 15 amps are variable, I think it just puts out 12.7 at 15amps, so the battery state will not alter what the charger does, it just does it no matter what. How the battery takes the power is different.
Am I missing something?
I will have to take actual measurements when I can plug it in and connect to a battery. I cut this out of my wrecked Rv a few years ago, but remember when I switched to the charger (not battery) that the lights got much brighter, so that suggest more like 14 volts than just 12.7 as batter would be12.4-12.6 at the same time…
The solar and MPPT are all that is needed to take care of the power, but on rainy days, or heavy shade, or cloudy short winter days I would like the option to supplement…