Methods are herein described for the assembly and electrochemical characterization of a Li+ battery consisting of a single microparticle (ca. 50 mum diam) of LiMn2O4 as the cathode, and a single spherical mesocarbon microbead (MCMB) as the anode, using either 1 M LiClO4 in ethylene carbonate EC/diethyl carbonate DEC mixture (1:1 by volume) or 1 M LiPF6 in EC/dimethyl carbonate (1:1 by volume) as the electrolyte. Self-discharge curves were recorded by monitoring the potential of the battery as a function of time after charging independently each of the microparticle electrodes to full capacity. The results obtained showed that charge retention is vastly superior for the LiPF6, compared to LiClO4-containing electrolyte, in agreement with results published elsewhere using more conventional devices. This behavior has been attributed to the chemical instability of perchlorate ion toward the charged cathode. (C) 2004 The Electrochemical Society.