An onboard battery is a small, built-in power source within electronic devices, such as computers, routers, or embedded systems. Its primary function is to retain critical information - such as BIOS/UEFI settings, real-time clocks, or encryption keys - when the main power supply is disconnected or turned off. In cybersecurity, onboard batteries help maintain secure configurations and system integrity by ensuring that essential settings and data are preserved even during power outages or intentional shutdowns. Failure or depletion of an onboard battery can lead to loss of configuration, system errors, or security vulnerabilities, making regular monitoring and timely replacement important for secure device operation.