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The main features of Lithium-ion (Li-ion) batteries are high energy and power density, which make this storage technology suitable for portable electronics, power tools, and hybrid/full electric vehicles. Moreover, during conditions that lead to failure, Li-ion battery cells could undergo into a process called thermal runaway, which has resulted in numerous fire accidents. Thermal runaway implies a rapid increase in battery cells temperature, accompanied by the release of flammable gases. These flammable gases could be easily ignited by the battery’s high temperature, resulting in a fire. In addition, the combustion of these gases when venting from the battery poses another safety concern: the accumulation and potential explosion of the gases themselves. Thermal runaway may also be responsible for mechanical effects such as the projection of fragments as well as the release of toxic gases and vapours. This study reports and discusses the results of fire tests performed on single Li-ion cells. Lithium Nickel Manganese Cobalt oxides cells from Panasonic were used in the tests. The tests were carried out in a cone calorimeter changing the state of charge of the cells and the radiant power of the conical heater. In order to assess the ignition and combustion characteristics, ignition time, mass loss, heat release rate and surface cell temperature were measured and recorded. The volatile organic compounds released during the tests were also measured by a photoionization detector. Since the appropriate fire prevention and protection measures have not yet been developed, this paper investigates the effects of thermal abuse conditions on Li-ion cells of battery systems for hybrid/full electric vehicles, in order to develop safe instructions and procedures for a rescue team that is called to respond to accidents involving these vehicles.