Reactant supply and effluent storage cartridges adapted for use with a closed liquid feed fuel cell system, as well as closed liquid feed fuel cell systems. The cartridge includes at least first and second volumes and comprises: a first reactant reservoir for holding a first reactant, the first reactant reservoir being configured to occupy substantially all of the first volume when filled with the first reactant; a second reactant reservoir for holding a second reactant, the second reactant reservoir being configured to occupy substantially all of the second volume when filled with the second reactant; and an effluent reservoir for holding effluent produced by the fuel cell system, the effluent reservoir being configured to occupy, when filled with the effluent produced by the fuel cell system, a portion of the first volume, a portion of the second volume, or a portion of the first and second volumes. The reactant supply cartridge of may further comprise an electrolyte reservoir for holding an electrolyte. In other embodiments, the present invention is directed to a computer system comprising the detachable cartridges and closed liquid feed fuel cell systems disclosed herein.