Battery-backed systems use a coin cell or small lithium battery connected to a low-power static RAM or clock chip. When the main power supply drops below a certain threshold, a supervisory circuit switches the chip's power pin over to the battery. This prevents the loss of configuration data or timekeeping during power outages or when a device is unplugged.
Heard on the job
The configuration is stored in battery-backed SRAM, so we'll lose our settings if we pull that coin cell.