An implantable medical device includes an enclosure sleeve and a top cap. The enclosure sleeve comprises an enclosure wall with at least a portion of the enclosure wall comprising the grade 5 titanium and having a thickness between 0.007 inches and 0.009 inches. The enclosure sleeve includes an open top end and an open bottom end that is opposite the open top end. The top cap includes a feedthrough block, a first top cap end portion, and a second top cap end portion. The first top cap end portion is configured to couple to the open top end of the enclosure sleeve, and the second top cap end portion configured to be positioned within the enclosure sleeve.