Hi Mike,
So the configuration I tried was to have the batteries positive terminal go to the top side of the load and the bottom of the load go through the FET to ground. I could get this to work but the problem is it only words for one battery. When more are added any of the MOSFETS being on will give the battery a path to ground. The voltage of each 4 series A123 pack is 13.2V. The load current will eventually be upwards of 30A pulsed but we will be happy to get 2-3A pulled now. We need to be able to pick which battery pack we interact with for the purpose of our project. One of three states, being charged, being used to run the load, and the last state is idle. The Vdd of the PIC is from 3-5V but we are currently running it off a separate power supply. A voltage regulator and PIC will the added to the load eventually. As for the Vss pin, I'm Sorry I dont know what you mean. The negative lead of the batteries is connected to the drain of the MOSFET through ground, which all the batteries go to. Thanks for you help.