What affect does removing the CMOS battery have and how to I change the settings back

[Silverthunder]

I did some research online and learned that when you remove the CMOS battery it will reset certain things.  But, exactly what this will reset and how to change it back (once you put the CMOS battery back in) to the "before removal state" can vary by computer.  I learned that you should look in the user manual to see how to change the settings back after you remove the cmos battery.  I looked in the user manual but it didn't seem to give this information. 

[Dark_Panther]

Hi welcome to HP Forum

We are happy to help you. 

The EEPROM is not the copy of the BIOS used to boot the OS or effect
settings. THe EEPROM defaults get copied into CMOS memory (hence why it
is called the CMOS battery). It is the CMOS memory copy that gets used.
When you make changes to the BIOS settings, you are changing those in
the CMOS memory copy. Some boards allow users to copy back the changes
in CMOS into the EEPROM to make those the defaults or provide a
user-config table to load by selection instead of having to make all the
selections again; however, most copy from EEPROM into CMOS and it is the
CMOS copy that you edit and that gets settings used from there.

So if the CMOS battery is dead then there is nothing to energize the
CMOS chip to retain its values. That means on every boot you will get
the defaults loaded from EEPROM. If the defaults prompt for user input
than that's why you're getting the prompt.

CMOS batteries typically last 5 years before needing replacement. That
is from the date of *manufacture*, not from when you received a computer
with a CMOS battery that was sitting in someone's inventory for a couple
years or you bought off the shelf (get those only if they specified an
expiration date, not how many years they last since you don't know how
old is the battery that is dangling on the shelf). It's good
maintenance practice to replace the CMOS battery about every 3 years to
ensure it is strong enough in voltage to retain the CMOS settings. You
typically have about 1, or maybe 2, minutes to put in a new battery
after removing the old one before the charge drains off the CMOS chip.

A dead CMOS battery is also the cause of why your computer won't retain
the *BIOS* time and date. Your OS might sync later with an NTP server
to get back on time but it first takes the date and time from the BIOS.
The RTC (real-time clock) chip is usually the same chip as where is the
CMOS memory to hold the changed settings of the EEPROM copy.

I hope this might helps you to know about the CMOS battry.

[mdklassen · Accepted solution]

> how to change the settings back after you remove the cmos battery. 

It's all in the "preparation".

Before you change the battery, use your smart-phone to snap pictures of all the BIOS SETUP screens, to make a record of the current value of the settings.  Or, "old-school" pencil-and-paper will work.

After you change the battery, use BIOS SETUP to change the settings to match the images on your smart-phone.

[Silverthunder]

Ok, great.  That sounds easy enough.

[mdklassen]

Welcome to this forum.

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