A study of LiCoO2/graphite and Li[Ni1/3Co1/3Mn1/3]O-2/graphite commercial cells cycling between narrow voltage limits near full state of charge on a high precision charger and stored at various voltages on a custom storage system was performed. It is demonstrated both theoretically and experimentally that narrow range cycling and storage experiments give direct information about the parasitic reactions occurring at the positive electrode in a Li-ion cell. The potential and temperature dependence of these reactions was mapped over the range between 3.95 and 4.2 V and between 30 and 60 degrees C. These techniques should be adopted by researchers and engineers looking to understand the function of electrolyte additives, new electrode materials and electrode material coatings in Li-ion cells. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.033302jes] All rights reserved.