What size panel do you have?? If it is a single 100 watt panel the mppt does not have enough room to adjust the voltage and current to get much more out of it than what you experienced. If you have a larger array, such as two 100 watt panels, connecting them in series or parallel gives much more room for the mppt to adjust either the voltage or the current to maximize the most amount of current to send to the battery.? My system is much larger but with it I can demonstrate what I mean above.? I have 400 watts of solar hooked up so that my voltage is approximately 43 volts & the current is 10 amps. Because I'm pushing to a 12 volt battery it can adjust the voltage down and the current up to put more energy into the battery. In this diagram from my system this morning, you'll see that the? current coming from the solar is 5.69 and the current going to the battery is 13.3
The voltages at the same time look like this second screenshot. When the current drops off in the top graph, that is when the battery is considered at 100% charged and it goes into the absorption cycle. At that phase of charging in a lead acid it is holding it there for a period of time at 14.4 volts to allow any sulfation that is happening in the battery plates to help drive it back into the electrolyte solution.?
Eugene Breindel