A new method has been developed to estimate the charge capacity of LiFePO(4). This method does not rely on assembly of active material, carbon and polymer binder composite electrodes, and can be used on nanoparticles with or without carbon coating. Charge capacity is derived from LiFePO(4) oxidation by a solution redox mediator, 10-methylphenothiazine, in a bulk electrolysis system. The mediator serves the role of connecting the working electrode with the LiFePO(4) particles suspended in the electrolyte. XRD and IR spectroscopy identified the oxidized species as heterosite-FePO(4), as in standard coin cell tests. Analyses with 6.8% relative standard deviation were routinely obtained. (C) 2011 Elsevier B.V. All rights reserved.