One conventional electrolyte (“Gen 2”) for lithium-ion batteries consists of 1.2 M LiPF6 dissolved in ethylene carbonate and ethyl methyl carbonate. A comprehensive investigation of this electrolyte in a high-voltage graphite/LiNi0.5Mn1.5O4 (LNMO) cell was carried out to evaluate its voltage stability under various charging conditions. Although the carbonate-based electrolyte was relatively stable when the graphite/LNMO cell was charged to 4.8 V at room temperature, the introduction of a constant-voltage charging step aggravated the oxidative decomposition of the electrolyte. Further increase in the cell charging voltage to 4.9 V or above and further increase in the temperature to 55 °C caused cell performance to deteriorate dramatically.