Attached a high level diagram of the circuit.
The green circled section is an already existing, tested and working battery charger product of mine.
The additional circuitry is being added to provide discharge and battery capacity capabilities to the charger.
I am not sure how to implement the current sense resistor. I initially decided I would design to share the current sense resistor and went ahead with that idea, I even found the LT1999 bi-directional current sense amplifier from LT to do the job of current sensing on a resistor in both directions. Then I realized that my feedback loop for controlling the FET as a load would need to connect to the node between the sense resistor and the battery -ve. Thus, with the opamp being referenced to ground the feedback loop would be feeding a slightly -ve voltage to the inverting input of the op-amp.
Is this going to work, or is there another way I am not seeing, to share the current sense resistor?
I could always just add another sense resistor, but I was trying to be slick and try to share the one sense resistor.