Stupid question - CMOS battery

[Coherence]

After building so many PCs, you'd think I'd know the answer to this. Perhaps I've just not had a single mobo long enough before upgrading to notice when the CMOS battery dies out. How long do the lithium button batteries generally last?

Since removing the battery will clear the CMOS, and the point of the battery is to keep that from happening, is there any way to replace the battery without having to reset everything? I can't imagine doing it while the system is turned on, of course. That could fry your system if you're not careful, I'd think.

It's a shame manufacturers don't make a mobo that has two battery sockets, so you can pop a new one into the empty socket before removing the bad one, that way you don't lose your CMOS settings.

Perhaps they just figure people will upgrade as often as I do, and will never have to worry about it. An associate of mine doesn't do that, though, and has noticed her PC losing time, which is a good indication of the battery going bad, hence the question.

 

[Arcanedeath]

In general 3 to 5 years as long as the PC is pluged in. Although some will last longer

 

[Zepper]

You can replace the battery while the machine is running - won't lose any settings. Just be careful not to drop it across critical circuits while removing it. Murphy's law...
. Losing time is not always a hint the battery is week - could be as simple as a complex screen saver eating up a lot of interrupts. One of my customers had a college football screen saver that ate so many interrupts, his faxmodem couldn't detect a fax coming in. Changed to one of the simple Win screen savers and it worked fine.
.bh.

 

[stevty2889]

The only CMOS battery I ever saw die, lasted 8 years.

 

[lenjack]

I didn't see your stupid question. Yours was a good one.

 

[JackHawksmoor]

The only one I've ever had die was in an iMac that was unplugged for half a year (and it turns out there was a BIOS update that fixed the specific problem of the CMOS battery running down to fast if unplugged).

I have ones in systems from '97 that still work.

This is a totally stupid tangent, but I HATED those Dreamcast VMUs that took two CMOS type batteries and ate through them in about 5 hours. What the hey? Those batteries are WAY too expensive to use like that.

 

[VirtualLarry]

Coherence, based on the mobo design, it is probably possible to replace the CMOS battery, while the system is on, without losing your settings, but why chance it? It's possible that during the insertion/removal of the battery, you might glitch them anyways. Plus, yes, you could also short out some part of the mobo and destroy something more valuable. It's usually not difficult to simply adjust the settings again, unless you have uber-tweaked manual RAM config info in there, in which case it's probably a good idea to print them out or write them down.

Plus, there are actually DOS programs that will save CMOS config settings to a file, and then restore them back. I don't know how well they work for modern mobos, but there used to be a tool in the old DOS Norton Utilities to do just that. It was part of the rescue disk that it would create for you too.

JackHawksmoor: I know what you are talking about, the batteries aren't that expensive, but they shouldn't be used up that quickly either. I have a PDA here that takes two sets of batteries, a pair of small hearing-aid size ones, and a pair of the larger ones (CR2016, the thinner version of the type used on PC mobos). It appears that they last on the order of 4-6 months in my PDA.

As for the lifetime of those batteries, they should last 3-5 years, as Arcanedeath stated, however I've been seeing more and more, some brand-new mobos seem to include batteries that have already used up a good portion of their "shelf life", and need to be replaced within 6-12 months after mobo installation. Disappointing, but not unexpected, due to the cost ("cheapness") of things these days. Once I replace them with a Duracell (about $1.50 worth of battery), they're usually good to go for as long as the person owns their PC for.

 

[Zepper]

Another option is to print out your settings screens before you chage the battery so you can re-do the settings. Some of the BIOS setups tell you which key combo to use to print the screens. Those that don't specifically say will usually work with just the PrintScreen key or sometimes Shift-PrintScreen or Ctrl-PrintScreen... But of course that may not work with today's Win printers...
.bh.