This paper deals with a life model for low voltage polyester- insulated capacitors subjected to time-varying temperature. The results of accelerated life tests performed on low voltage polyester-insulated capacitors at various temperatures are illustrated and from them a constant-temperature life model is derived. Such model, inserted within a “Miner’s law” framework, gives rise to a variable-temperature life model that is compared with the results of subsequent life tests performed on the same kind of capacitors under daily temperature cycles. This is a milestone towards real-time life estimation of capacitors subjected to time-varying temperature, as well as towards the extension of this approach to other electrical devices.