CR2032, or, how to lose a day for $1.75

10 Jul 2008 by mjc, No Comments »

Anyone who has looked inside a computer has probably noticed that PC motherboards have a battery plugged into them.  This battery is responsible for keeping alive the memory that holds the BIOS settings.  When the battery goes flat, those settings are lost, and the next time the computer boots, it has forgotten about things like what hard disks are connected, or the frequency at which the clock should run.

In most of the PCs I have worked with over the years, that’s about all that happens — it’s annoying, but each time the computer boots it has lost its settings.  In servers, which don’t reboot often, a flat battery could go unnoticed for months.

Yesterday, I discovered that some PCs are far less predictable when the motherboard battery is flat.  I have four ~5-year-old Shuttle PCs, and some of them haven’t been turned on for a year or so.  What *they* do is not start at all once the battery is flat.  But if you leave the mains power connected for a while, eventually something gets enough charge that the motherboard decides it can boot after all.

In addition, with a battery on the way out, the PCs would get part way through booting and then freeze in random places.  This took some time to discover — I was initially suspicious of a recent operating system upgrade, and then that a disk might be on the way out.

To keep a long story from getting any longer, the lesson learned was that it’s worth spending $1.75 every 2-3 years to keep a charge in that battery.  Once it goes flat, odd things can happen.

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