I made a charger using a TI BQ2031 IC and it regulates current at Imax until Vmax is reached, then regulates Vmax until current falls to a set percentage of Imax so for a 12 volt 4Ah battery I regulate current at 1C until voltage reaches 14.7 volts, and then maintain 14.7 volts until current falls to .25 amps. Then I switch to a float charge of 13.5 volts to keep the batteries topped off. When it is regulating the voltage at 14.7 volts, current will slowly fall as the battery charges. For MPPT they have this app note: http://www.ti.com.cn/cn/lit/an/slva378/slva378.pdf