Some examples of an electrical contact spring for an implantable medical device includes a housing, rigid and tubular in shape, defining a housing passage extending along a longitudinal axis, from a proximal portion including a proximal lip that defines a proximal opening, to a distal portion including a distal lip that defines a distal opening and a spring disposed in the housing, the spring tubular in shape and defining a spring passage concentric to the housing passage, the spring including: a distal ring portion disposed adjacent the distal portion of the housing and physically coupled to the housing, a plurality of spring elements coupled to and extending from the distal ring portion toward the proximal portion of the housing and a proximal ring portion disposed adjacent the proximal portion of the housing, cantilevered and suspended inside of and spaced apart from the housing by the plurality of spring elements.