Wearable devices face a significant challenge in balancing battery life with performance, often leading to frequent recharging and reduced user satisfaction. In this paper, we introduce the SmartAPM (Smart Adaptive Power Management) framework, a novel approach that leverages deep reinforcement learning (DRL) to optimize power management in wearable devices. The key objective of SmartAPM is to prolong battery life while enhancing user experience through dynamic adjustments to specific usage patterns. We compiled a comprehensive dataset by integrating user activity data, sensor readings, and power consumption metrics from various sources, including WISDM, UCI HAR, and ExtraSensory. Synthetic power profiles and device specifications were incorporated into the dataset to enhance training. SmartAPM employs a multi-agent deep reinforcement learning framework that combines on-device and cloud-based learning techniques, as well as transfer learning, to enhance personalization. Simulations on wearable devices demonstrate that SmartAPM can extend battery life by 36% compared to traditional methods, while also increasing user satisfaction by 25%. The system adapts to new usage patterns within 24 h and utilizes less than 5% of the device's resources. SmartAPM has the potential to revolutionize energy management in wearable devices, inspiring a new era of battery efficiency and user satisfaction.