A modular battery pack system including a plurality of battery sub-modules operably connected in parallel and an isolation system configured to discretely isolate any one of the battery sub-modules from the remaining battery sub-module(s). The isolation system, in one embodiment, may utilize an ORing FET for each of the battery sub-modules, with each ORing FET operably connected at its input with an output of a corresponding battery sub-module and operably connected at its output with the output of the other ORing FETs. The modular battery pack system may further include a conditioning system for conditioning a battery sub-module by discharging at least a portion of the battery sub-module. Each battery sub-module may be operably and discretely connected to the conditioning system, such that conditioning is selectively applicable to any one or more of the battery sub-modules.