Commercial battery cells with Li4Ti5O12 negative electrode and composite metal oxidepositive electrode have been analyzed with respect to ageing mechanisms. Electrochemical impedancespectroscopy (EIS), differential capacity analysis (dQ/dV), differential voltage analysis (dV/dQ) andscanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) were used to identifydifferent ageing mechanisms such as lithium inventory loss, loss of active electrode material andsurface film growth. The active material of the positive electrode was also examined by X-raydiffraction (XRD). Ageing mechanisms were studied for both calendar-aged and cycle-aged cells. Datafrom half cells prepared from post mortem harvested electrode material, using lithium foil as negativeelectrode and pouch material as encapsulation, were used as reference to full cell data. Electrochemicalanalysis of full and half cells combined with material analysis showed to be a powerful method toidentify ageing mechanisms in this type of commercial cells. The calendar-aged cell showedinsignificant ageing while the cycle-aged cell showed noticeable loss of positive electrode activematerial and loss of cyclable lithium, but only minor loss of negative electrode active material. Theresults imply that Li4Ti5O12 negative electrode material is a good alternative to other materials if highenergy density is not the primary goal.