Sensor circuit/product designing to measure SOC/Capacity for Lithium Ion battery packs

Hi, we need a simple sensor for our datalogger to measure capacity/state of charge (SOC) for 48v DC lithium ion phosphate battery packs - ranging from 10ah to 100ah in sizes. The unit/circuit MUST be able to output the signal as 3.3V. We have seen 100v coulometer lithium sensors and use of a shunt resistors to do this out on the internet but these are all to send data to an lcd screen and we need to find a solution very quickly. So can you help? We will need a design including material/product details in order to make one ourselves. Many thanks, Mark