Replacing a CMOS battery

Greetings all,

I have an old Compaq Presario 4862 in which the CMOS battery recently died and I can't seem to find anyone that carries a replacement for it, in the physical world or online. I am curious if a watch battery would work as a replacement if one could be found with the same specs or could someone direct me to a source where I could get a new one.

Yes, I know the computer is obsolete but I also have an Olivetti with an 8086 processor and an external 40MB hard drive that's the size of a 13" TV (although it doesn' get much use) and I want to keep the Compaq as my DOS gaming rig.

Thanks

 

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If the specs (and size) are the same, there should be no problem.
Most CMOS betteries aren't too difficult to find replacements for.
Are you looking by computer model name, or the number on the battery itself?
What is the battery number (usually engraved on the "top")?

 

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Hi one raven,

I have been searching by computer name, haven't had a chance to pull the battery out yet. The computer still boots so I didn't find it that urgent. My thinkpad did the same thing when it's CMOS battery died (booted fine after I re-entered the CMOS settings) for a few weeks before going belly up. So I figure I have a little time before it becomes desperate.

Thanks

 

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There's a good chance it is a fairly standard size that you can get at adio Shack for three bucks.
CR2032 is a very popular one for CMOS.
Read the battery, and run the number on it (if Radio Shack does't have the same number in stock) and you are likely to find a suitable replacement.

Be very careful taking it out!
If you haven't done this before, be warned that a lot of the old computers did not have spring mechanisms holding the battery in, and it is VERY easy to break the arm that's holding the battery in.
Slide it out, DO NOT pull it up.

Also, Lithium batteries lose 1/2 their life if you touch them.
Use a paper towel, or wear linen gloves or do something to avoid touching the battery directly.

 

Hi one raven,

Thanks for the heads up. I did replace the battery on my thinkpad with no problem but I did not know about the loss of battery life by touching a lithium. I will definitely keep this in mind. The idea of a watch battery just occurred to me earlier today, so I wasn't sure if it was possible. I really appreciate the info you have given me. I thought I was an ubergeek when it came to hardware but it looks like I still have a lot to learn, even on the old.

Thanks

 

some mobo's have 2 pins that you can attach a replacement CMOS battery.
a standard 1.5v AA or AAA will work in cases such as this.

i wonder why computer manufacturers don't use a rechargeable battery for cmos? when the computer is on the battery is recharged, or even better that the cmos is powered from the computers supply when on.

anyway good luck with your cmos.

Hmmmm . . . i never heard anything like that before. you sure?

 

Hi leopold99,

Thanks for the info, I will look into my mobo's specs and see but I think it might be too old. I've also wondered why they aren't rechargable.

Thanks

 

I was taught this when I worked for Radio Shack many years ago, and then told again when I was in computer school.

I can't say that I am 100% certain, but this has been my practice for about 20 years now - it could very well be moot.
I will look for some "official" reference for you.

 

A computer will continue to work with a bad CMOS battery; but all settings will revert to defaults whenever it is powered off.

Many older Socket 7 boards had a rectangular plastic component that says RTC with a little clock symbol on it. I took one apart once, and there is a battery inside, about the size of a hearing aid battery. You should be able to find a replacement.