well, i guess i missed that little detail in the schematic. I used the voltage from Vb to power the PIC (VDD) and also used the same common ground for Vss. I'm making a battery charger and basically i want to take the voltage measurement at Vb while there is no current going into the battery from the outside voltage source Va (i want to do this because the voltage of the battery increases while the current is going into the battery, however when the current is removed i can measure the voltage of the battery and it will be closer to the open voltage.)

I hope this makes a little more sense.