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CMOS battery

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ajaysrana   09-23-2009 at 04:26:20 PM

Hello,
I got a desktop computer which will loose its BIOS settings, if i leave it unplugged for more than 6 hrs. After this i have to reload the BIOS settings. I can't have default settings because it is a special application computer which i am using. Battery have been changed several times with no success. Any suggestions would be highly appreciated.

Thanks
Ajay

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Bronze Motherboards badge o1die   09-23-2009 at 07:27:01 PM

Why do you leave it unplugged? That will run down the motherboard battery quicker. Look inside and see if your board battery is round. Many use the 2032 Lithium battery, which go for about $2-3 at walmart or target, last time I checked.

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ajaysrana   09-23-2009 at 08:06:41 PM

It is a CR2032 battery. And that battey i have changed it 2-3 times already with no effect. Normally motherboard battery should hold the BIOS settings and if it is not there must be something which is draining this CR2032 battery out so fast. The voltage of this battery i have also measure, it is 3.5 V and that is also as per spec. It appears some component in motherboard is bad. Do you think of anything else what could be causing this issue.

Thanks for ur help
Ajay

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Pointertovoid   09-25-2009 at 01:09:07 AM

Read once that finger sweat on Cmos batteries can increase current leakage. It sounds reasonable to my electronics ears, but certainly not down to 6 hours.

However, I could imagine that just an electrolytic capacitor is able to power the Cmos Ram for 6 hours: already seen one keeping its data for >20min without a battery.

So maybe the battery isn't connected at all with the Ram (battery sockets are often bad). Could you find the pinout of your Cmos Ram and check the voltage on the supply there? Comparing it with the battery may tell something.

Also, what's the battery voltage after the Ram loses the settings? You told 3.5V, is it before inserting the battery or after data loss?

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