Na+/H+ antiporter that extrudes Na(+) or Li(+) in exchange for external protons across the membrane. Contributes to the regulation of intracellular pH, Na(+) content and organellar volume. Plays an important role for insulin secretion and clathrin-mediated endocytosis in beta-cells. Involved in sperm motility and fertility. It is controversial whether SLC9B2 plays a role in osteoclast differentiation or not (By similarity). Strong colocalization with LAMP1 and TCIRG1 in osteoclasts. In beta-cells colocalizes with RAB4A and SYP. Localizes to the basolateral membrane of polarized osteoclasts. Inhibited by phloretin but not the classical SLC9A-inhibitor amiloride. Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family.