Electric medium- and heavy-duty vehicles (eMHDVs), compared to their gasoline counterparts, are a promising solution in alleviating the global dependence of fossil fuel energy usage in the transportation sector. However, increased vehicle mass due to energy storage and powertrain upgrades require research and development efforts to improve eMHDV performance. Addressing power and voltage requirements of the powertrain, HV battery, and auxiliary loads can facilitate a bridge towards the metrics of conventional MHDV builds. DC-DC converters utilized in the on-board charger (OBC) and auxiliary power module (APM) of an eMHDV are therefore the focal point of this article, wherein a three-port converter (TPC) arises. To lay foundation, opportunities for OBCs across the wide spectrum of eMHDV models, vocations, and masses are identified through a study based on available specifications from 93 state-of-the-art (SOA) vehicle models, combined with 23,000 days of fleet data. OBCs are deemed feasible for eMHDVs due to long available off-shift charging times coupled with SOA battery capacities. Elevated power requirements of high-voltage and low-voltage auxiliaries in eMHDVs are also outlined. Then, TPCs are compared to conventional DC-DC converter solutions in terms of volume, efficiency, and cost. Despite elevated OBC and APM power requirements, TPCs are concluded to not be a limitation in eMHDV applications. Finally, a topological based review of SOA TPCs is performed outlining key technological gaps, design requirements and recommendations, and future research required for expansion to eMHDVs.