Electrified vehicles may be powered by traction battery packs. An exemplary traction battery pack may include an enclosure assembly having a tray and a cover. One or more hinged locking plate assemblies may be utilized to secure the cover to the tray of the enclosure assembly. The hinged locking plate assemblies may be configured to exert a clamping or compression force across an interface between the cover and the tray, thereby enhancing retention and providing a leak-proof joint.