So from my understanding form a code perspective all I need to do is set PWM value such mosfet sees 4V at gate such that current is limited to .1A. And taking the datasheets average value of charge voltage for cycle use for 6 cell battery is how I came up with 14.7V so it would seem that's correct.
No, there are a lot of variables, temperature, mosfet threshold voltage, battery state, you can't control a current by setting specific voltage. Better to measure current itself, and adjust voltage accordingly to keep 0.1A. Charging chart shows 13.8 V as max voltage and they recommend constant current / constant voltage as a method of charging. It looks like it takes only 7 hours for fully discharged battery to get up to 13.8 V ( current exact 0.1A) and after that current drops but voltage stays 13.8 V, if it's me I wouldn't reinvent a wheel and follow their recommendations