Abstract: System and method for predicting the remaining useful life (RUL) of a rechargeable battery, such as a lithium-ion rechargeable battery. In a method, the capacity of the battery is determined based on at least changes of state of charge values estimated at a first and second time and a net charge flow of the battery and applying a particle filter to a capacity degradation formula using the determined capacity to form a capacity degradation model and determining the RUL using the capacity degradation model using a pre-defined end of service threshold. The system and method may be used to predict the RUL of a rechargeable battery in an implantable medical device.