Long-term charge injection and extraction cycling performance of electrochromic devices, and the degradation of the devices has been studied. The electrochromic devices have been constructed using sol-gel deposited tungsten oxide layer, sol-gel deposited vanadium oxide layer and a polymer electrolyte. Both electrodes were cycled in a solution of 1 M-LiClO4 and propylene carbonate prior to device fabrication. The devices were sealed using a rubber O-ring so that disassembly and further electrochemical and optical testing of each component after use in a device could identify the reason for device degradation. During the tests, the charge state of the device and device transmittance were recorded by a computer controlled experimental system. The results show three main modes of degradation, which we have denoted as electrolyte failure, counterelectrode failure and working electrode failure. Each failure mode can be identified on a device history graph which shows charge and the ratio of transmittance in the bleached to the transmittance in the coloured state (contrast ratio) as functions of cycle number.