This small battery is on your computer's logic board, and it helps NVRAM retain settings when your Mac is unplugged. If you're using a desktop Mac instead of a notebook, and settings such as sound volume or time zone are reset every time you shut down and unplug your Mac, you might need to replace the battery inside your Mac.When your Mac finishes starting up, you might want to open System Preferences and adjust any settings that were reset, such as sound volume, display resolution, startup disk selection, or time zone. To reset NVRAM, first turn off the firmware password. If your Mac is using a firmware password, this key combination does nothing or causes your Mac to start up from macOS Recovery.
Settings that can be stored in NVRAM include sound volume, display resolution, startup-disk selection, time zone, and recent kernel panic information. PRAM (Parameter RAM) stores similar information, and the steps for resetting NVRAM and PRAM are the same. NVRAM (nonvolatile random-access memory) is a small amount of memory that your Mac uses to store certain settings and access them quickly. If your Mac has issues related to settings stored in NVRAM or PRAM, resetting it might help.