This paper quantifies the low-temperature capacity and energy losses of LCO and LFP cells and matching battery packs tested under the legacy USABC protocol at room temperature and 0 °C. The work establishes chemistry-dependent capacity retention, discharge-voltage depression, apparent resistance increase, and cell-to-pack derating factors using a compact experimental matrix. A simplified Matlab/Simulink pack model, parameterised from room-temperature and 0 °C discharge curves, is introduced to reproduce the observed pack-level capacity loss with minimal electrochemical assumptions. The model is intentionally transparent: it maps temperature-dependent open-circuit voltage, internal resistance, and usable capacity limits to pack voltage and energy estimates. The paper’s contribution is a validated baseline showing how much accuracy is achievable with a generic battery block before detailed electrothermal modelling is justified. The results provide a common reference for cell-to-pack and thermal-management studies across a wider range of chemistries and pack architectures for automotive applications.