Electronics subsystems for monitoring, control, and enhanced functionality play an increasingly important role in safety critical systems. Electrolytic capacitors are an important component in several key subsystems that range from power supplies on safety critical avionics equipment to power drivers for electro-mechanical actuators. These capacitors are known to have comparatively low reliability, and given their criticality in electronics subsystems they are a good candidate for component level monitoring and prognostics. Prognostics provides a way to assess remaining useful life of components and systems based on their current state of health and their anticipated future use and operating conditions. Past experiences have shown that capacitor degradation and failures are quite prevalent under high electrical and thermal stress conditions that they are often subjected to during operations. Our focus in this work is on deriving a physics-based degradation model for electrolytic capacitors under thermal stress conditions. As part of our methodology, we study the effects of accelerated aging due to thermal stress on a batch of identically manufactured capacitors operating at different temperatures. This provides a framework for supplementing theoretical modeling with data collected from simultaneous experiments, which is then used to validate the derived models.