Vehicle electrification is driven globally due to the increased concerns on carbon emissions. But the challenges in customer acceptance remains esp. in relation to vehicle costs. Virtual simulations can help in cutting down product development cost and enable faster launch of new vehicles. An early stage system model based design iterations can help in cutting down the product development costs and building more robust products. In the current paper, we develop and analyze a battery pack system model for early phase design. We extend a previously developed system model to include critical physics like sub-component level multiphysics for electrical joint integrity. Also, we demonstrate an integration of 3D FEM & system model for improving the accuracy of joint temperature predictions during charging and/or discharging. A typical High Voltage (HV) battery system comprises of battery modules (Li-ion cells, cooling channels, structural frames, interconnect boards) and HV bus bars. Multiple modules are connected together to form a battery pack or a Rechargeable Energy Storage Systems (RESS). In the current paper, we have built an enhanced system model with 3D FEM simulations incorporated to evaluate the HV system performance during constant current charging scenarios and temperature at different components of the system. Proposed methodology would help to quickly simulates different design iterations in reduced order system model with built in transfer functions available from 3D FEM.