The operation of deep-sea underwater vehicles relies entirely on onboard batteries. However, the extreme deep-sea conditions, characterized by ultrahigh hydraulic pressure, low temperature, and seawater conductivity, pose significant challenges for battery development. These conditions drive the need for specialized designs in deep-sea batteries, incorporating critical aspects of power generation, protection, distribution, and management. Over time, deep-sea battery technology has evolved through multiple generations, with lithium (Li) batteries emerging in recent decades as the preferred power source due to their high energy and reduced operational risks. Although the rapid progress of Li batteries has notably advanced the capabilities of underwater vehicles, critical technical issues remain unresolved. This review first systematically presents the whole picture of deep-sea battery manufacturing, focusing on Li batteries as the current mainstream solution for underwater power. It examines the key aspects of deep-sea Li battery development, including materials selection informed by electro-chemo-mechanics models, component modification and testing, and battery management systems specialized in software and hardware. Finally, it discusses the main challenges limiting the utilization of deep-sea batteries and outlines promising directions for future development. Based on the systematic reflection on deep-sea batteries and discussion on deep-sea Li batteries, this review aims to provide a research foundation for developing underwater power tailored for extreme environmental exploration.