The objective of this study was to highlight the usefulness of micron-sized Li4Ti5O12 in three distinctive areas: a) cathode of a low-voltage Li battery, b) insertion type auxiliary electrode to investigate the electrochemistry of oxide cathode materials, and c) anode of a Li-ion cell in conjunction with LiMn2O4 cubic spinel cathode. Li cells with Li4Ti5O12 exhibited an open circuit voltage of ∼1.6V, >90% utilization (in terms of the theoretical capacity) at ∼C/10 rate, ∼40% utilization 5C rate, and extended full-depth charge/discharge cycling at ≥ 1C rates with virtually no capacity fade. LiMn2O4 cathodes, evaluated in Li(4+xTi5O12 (x = ∼1.2)/LiMn2O4 cells, exhibited extended full-depth cycling capability with a small capacity fade rate of <0.1% which appeared to slow down with cycling. At a 1C discharge rate, over 190 cycles were demonstrated corresponding to an end utilization of ∼90 mAh/g or ∼0.6 mole Li per LiMn204. Balanced Li4Ti5O12//solid polymer electrolyte//LiMn2O4 full cells of slightly cathode-limited configuration had an open-circuit voltage of ∼3.0V and a mid-discharge voltage of ∼2.5V showing full-depth extended cycling capability at a utilization of ∼90 mAh/g or ∼0.6 mole Li per LiMn204 at the 1C and ∼0.45 mole Li per LiMn2O4 at the 7.5C discharge rate.