The 12V advanced start stop systems can offer 5-8% fuel economy improvement. Although the fuel economy improvement is not as high as those of mild to full hybrids, its low implementation cost make it an attractive fuel economy saving solutions. As a result the 12V advanced start stop technology has been evolving fast in recent years. On one hand, battery suppliers are offering a variety of energy storage solutions such as stand-alone lead acid, stand-alone LFP/Graphite, dual batteries of lead acid parallel with NMC/LTO, LMO/LTO, capacitors, and NMC/Graphite, etc. For dual battery solution the architecture also vary from passive parallel connection to active switching. On the other hand OEM are considering to leverage lot more use out of traditional 12V SLI (start, light and ignition) to functions such as power steering, AC conditioner, heater. Depending on battery architecture and function design the energy management strategy can easily become complex. Since many variables are involved in the design of 12V advanced start stop systems, an integrated simulation tool with a couple of modularized models including vehicle, battery systems, and performance characterization have been developed. The modularized tool would help to evaluate many aspects of the design from motor size selection, power network management, battery evaluation, testing standardization. As a specific demonstration, in this work, we use the tool to compare three chemistries: stand-alone AGM, stand-alone LFP, and dual batteries of lead acid and LTO for different driving cycles including NEDC, WLTP, FTP72, and HWFET as function of motor size.