Computer Time and Batteries

Ever wondered how a computer knows the time when you first switch it on, even if there’s no internet access?

It’s because there’s a battery in the computer that provides enough power to the motherboard for it to keep track of the current date and time, even when the computer is off. This is known as the CMOS Battery and is typically a coin battery of the type used in watches.

Because of this, a computer is always partially on, even when powered off, disconnected from the mains, and kept in storage. In addition to tracking the time and date, this is also how the computer retains the startup settings used to boot the computer into the operating system.

This battery is not rechargeable, so it will eventually go flat. The most obvious sign of a flat CMOS battery is having the time and date reset when powering on the computer. In addition to being annoying, this can also play havoc with software and backups that need to track time and date. As the CMOS battery is also used to keep the boot options consistent, a failing CMOS battery can result in a computer having problems starting up or drivers not being installed or configured properly. If any of these issues occur, replacing the CMOS battery may resolve the issue. The position of the CMOS battery varies from computer to computer and replacing it can be tricky, as it’s not always in an easily accessible position. If you need help with a computer that is showing these symptoms, or you know or suspect that the CMOS battery needs replacing, just get in touch.