I was planning on using the low pass filter to turn the pwm signal into a pseudo Digital to Analog converter. And the transistor is not logic level but data sheet for battery specified charging current of 100mA so setting the MOSFET to threshold voltage (4V if I remember) would allow about 100mA per the MOSFET data sheet.
I am aware the MOSFET will get hot and expecting to need a heat sink of some kind.
And ok good to know I had the resistance thing backwards but from my understanding the current will decrease as the battery charges at a constant voltage.
My biggest question is when I am providing the constant current what voltage should that current be at (the full charge voltage of 14.7?)