Message "la batterie CMOS est défectueuse ou a été récemment remplacée"

Hello,

"the CMOS battery is bad or was recently replaced"
As said, the battery is likely bad (too empty if it has been sitting for a while and cheap, it's common).
Improperly installed or broken is also possible.
And after replacement, you set the time and date and save it.

"I encountered an error that I didn't know and can't resolve. It all started with an error like 000000xxx your PC has encountered a problem"
Without knowing the precise error and who gives it, who knows...

"I have to be in legacy mode to boot from my Windows 10 USB key"
You need to create your USB stick in the correct format (GPT UEFI)

"Everything works in legacy mode"
That's not normal and not clean, this UEFI PC should be installed in UEFI mode.

"The problem is that I start the next day and this message appears and I am back in UEFI"
We're back to the battery

"Should I reset the BIOS?"
It's useless and it already happens when changing the battery.

"I am a self-employed IT professional"
Very surprising given the imprecision of the information, testing, installation...
Self-taught?

Start by buying a battery and replacing it.
We'll be sure at that level.

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Already see this story about the BIOS not keeping its settings
(I am reposting the questions here)

No visible case, small battery contact strip?
After changing, did you set the BIOS time and date and save it?
Does the date and time stay correct?

Then the installation part

1 > Download the ISO /
.
(no matter which PC you use to do this)
An ISO is a disk image, but for now, do not click on it.
It's a resource that we'll use to create a USB installation drive. We need to mount this image.

ISO W 10 x 64 home and pro (link valid for 24 hours)
https://software-download.microsoft.com/db/Win10_1903_V1_French_x64.iso?t=cd7b3380-7bfa-47c8-828b-0b2d3887f499&e=1571082489&h=12473c13717ea66b55a625be779408d6

Note:
the ISO can also be retrieved with Media Creation Tools, the Microsoft tool.
The provided ISO is always the most recent, up to date, so redo your installation key regularly to keep it "up to date."
It’s preferable to take the ISO and create your key with the following software to best manage the settings for the PC to repair.

2 > Create the installation key /
.
Download the Rufus software:
https://www.commentcamarche.net/telecharger/utilitaires/19615-rufus/


> Basically, point to the USB key that we will use (8 GB or more)
Be careful, empty your key before as everything will be erased from it.
> point to the ISO file you just downloaded
> set the partition type. (GPT as in the image)
> Start the creation and wait for the completion message.

3 > Boot your PC to repair from your installation key /
.
BIOS set to UEFI (and nothing else but UEFI, no CSM or legacy mode activated)
and
disable secure boot
(to disable if the PC does not boot from the key)
Confirm by exiting (F10 and confirmation)

Turn off the PC
Plug in the key
Restart
The PC should boot directly from the USB key, thus starting the installation.
If there are issues
We'll see together.

4 > Installing Windows /
.
Here’s an overview for W 10 (not really up to date but it’s just an overview)
http://www.windows8facile.fr/installer-windows-10/

I’m not sure what kind of installation you are planning to do.
If recovering, do it first with the help of a live.
Or reinstall only on the main partition where the system is, if it still exists, and the documents should be found in Windows.old after installation.
etc

If clean and nothing to recover:

You will start with a "custom" installation
You will follow the procedure and arrive at a screen that will list the locations and ask you "where to install Windows."

At that point, there are different possibilities:

> reinstall on the system partition, or delete some or all partitions etc... depending on whether you are recovering or not

or

> You can also wipe the entire disk before installing (and if the HDDs are not or are no longer GPT)
Press the Shift and F10 keys
(the command prompt opens)
Enter the following commands one by one, confirming with Enter:
diskpart
list disk
sel disk X (replace X with the number corresponding to your hard drive to be erased)
convert gpt (if the disk is MBR and you get an error like this when you want to install)
clean
exit
exit

Result -
Clearly, we wipe the disk and then return to the installation screen.
You will have only one volume to choose for the installation.

The installation proceeds.

Remove the USB key at this restart
(at worst, if it doesn't appear at this point and the PC has restarted from the key, you can remove it abruptly and the rest of the installation will continue)

5 > Once installed, a few points will need to be checked /
.
If activation OK
And
If drivers OK

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