A headspace insulator for a battery cell operatively coupled to circuitry within an implantable medical device in including one or more of the following: (a) a body of electrically and thermally insulating material disposed between a battery electrode assembly and a battery cover, (b) a receiving area within the body that receives and isolates a battery feedthrough pin, (c) an indentation within the receiving area retaining the feedthrough pin within the receiving area, (d) a raised portion coupled to a battery cover providing an air gap between the cover and the headspace insulator near case-to-cover weld areas, (e) a feedthrough aperture adapted to receive a feedthrough assembly, (f) a pin aperture that receives the feedthrough pin, (g) a fillport aperture for electrolyte fluid flow through the headspace insulator, and (h) a slot that locates a battery weld bracket and isolates it from the feedthrough pin.