Abstract: An exemplary modular energy storage system is disclosed. The modular energy storage system may include an enclosure, a plurality of battery modules positioned within the enclosure and operatively connected to a high voltage connector accessible from an exterior of the enclosure; a battery management system positioned within the enclosure, the battery management system including at least one contactor; and an air plenum positioned within the enclosure. Air may enter at least one inlet in the enclosure, passes through the air plenum, across a plurality of heat sink fins associated with the plurality of battery modules, and exit through at least one outlet in the enclosure. The at least one contactor may positioned within the enclosure to a first side of the plurality of battery modules and above the at least one inlet. An exemplary endplate for a battery module having a plurality of battery cells is also disclosed.