<p>This study investigates the heating (i.e. discharging) of Lithium-ion (Li-ion) polymer batteries (e.g. pouch and 18650 cells) embedded in sandwich composites made of carbon fibre laminate facesheets and polymer foam cores (Polyvinyl Chloride or PVC, Polyethylene Terephthalate or PET). The effects of facesheet thickness, foam core thickness and density, and battery type and orientation on the heating of sandwich composites are systematically investigated. Heat can be rapidly dissipated from sandwich composites when the Li-ion polymer battery has a large area of contact with the carbon fibre facesheets. However, rapid internal heating, potentially leading to thermal runaway and fire, may occur when the battery is fully embedded within the foam core and physically separated from the facesheets. The optimal foam core thickness to prevent overheating can be predicted using the numerical thermal design maps. This study builds on our previous work which investigated the thermal performance of monolithic carbon fibre laminates.</p>