When to replace CMOS battery in dormant machines?

  Aitchbee 14:00 21 Dec 2017

I want to revive some second-hand computers that have not been switched on for 2 years or more. Most have Windows 7 operating system already installed and all bought as seen, from several reputable computer shops or from charity shops etc, ... about 6 desktops and 3 laptops in all.

Should I replace all of their batteries before powering them up or is there a better time to do this?

  wee eddie 14:32 21 Dec 2017

The cost of a large pack of CMOS Batteries is not that significant.

What are you expecting to use them for and is about £1, too much to spend, per PC

  Aitchbee 14:42 21 Dec 2017

wee eddie, my request is solely to ascertain the optimum procedural time and conditions relating to the age of these computers for replacing the battery. My main concern is the fatal loss of Bios settings.

btw, I'll use these computers for mundane recording and archival purposes.

  Forum Editor 14:43 21 Dec 2017

I have often switched on computers that have sat idle for longer than that without any problems.

Just try it, then, if it's evident that something is wrong, replace the batteries. You'll know pretty quickly.

If cmos power is absent there's nothing 'fatal', the machine will still boot, but BIOS settings will reset to default.

  Aitchbee 14:45 21 Dec 2017

... if I can get them to work ;o]

  Aitchbee 14:49 21 Dec 2017

FE, that sounds reasonable to me. Only, as I've mentioned above my concern is losing Bios settings when the battery is removed. Do I keep the power on when I'm replacing the battery?

  Fruit Bat /\0/\ 15:06 21 Dec 2017

Do I keep the power on when I'm replacing the battery? I wouldn't, dropping the battery on to a live motherboard could sort out something vital.

Far better to make a note of the BIOS settings before changing battery and then resetting the BIOS after the change.

  Aitchbee 15:18 21 Dec 2017

OK, Fruit Bat. I'll do what you say. I was wanting to batch-renew/refresh 'em all at the same time for handiness and future reference. I'll 'revive' them one at a time.

Thanks all.

  qwbos 16:48 21 Dec 2017

If you're thinking about buying CMOS batteries in bulk (5 or 10 packs) be careful where you get them from and check them carefully before installing.

Clues to look for are mis-spelling on the packaging, lack of perforations on blister packs, suspiciously long use by dates and, if you're lucky, leaky cells.

There were huge numbers of counterfeit Maxell sellers on ebay for a while.

  Aitchbee 17:03 21 Dec 2017

Thanks, qwbos. I buy them from aldi or lidl. I know from experience that the ones they sell are far superior to other cheaper outlets like poundland etc.

  qwbos 00:58 22 Dec 2017


I got caught out some time ago by one of an apparent gang on ebay. The address of the sender led back to a high street shop that appeared to be offering all sorts of financial advice, including, apparently, fraud.

This thread is now locked and can not be replied to.

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