Dell Precision 7540 - replacing CMOS /RTC battery is unbelievably arduous

Here is the Youtube video that helped me locate all the screws that need to be removed.  

https://www.youtube.com/watch?v=MyRAUDmSebQ

Another good video showing the locations of all the screws that need to come out.  This is the 7530 model which is very similar to the 7540.

https://www.youtube.com/watch?v=YQfApUGbJSU

Hey, a bit late to the party, but what’s the cmos battery number. I am trying to order some and i see conflicting results from cmos-4 to cmos-41. 

@Hajikhapri​ I ordered mine from Rome Tech Batteries.  The important thing is to get the battery with the right connector.

Enter your PC model # on their website to find the correct one:

https://rometechbatteries.com/

@PCbluesky​  thanks. It was the regular cmos battery for all Dell laptops that i got. And it worked

the lowdown

The PDF Manual I have from this very website for my exact machine, which is a Precision 7540 Regulatory Model: P74F / Regulatory Type: P74F002, lists the CMOS battery as an ML1220. However when we go to the previously mentioned website https://rometechbatteries.com/ it specifies the CR 2032 as the the battery for both P74F002 and P74F001 variances of the Precision 7540. Making an already project even more of a pain.

Now I dunno but I read that the difference between an ML and CR coin battery is that the ML is rechargeable and the CR is not. This came from a distributor on Amazon selling ML1220 for Dell Precision machines. This was their statement "Note: The ML1220 battery of this product is a rechargeable battery, not a CR1220 disposable battery (voltage above 3V). When the ML1220 battery is not fully charged, the voltage is about 2.75V. The fully charged voltage is 3V."

From what I gather laptop coin batteries are NOT typically the rechargeable type and are most often the CR2032. You may have read that many Dell models, particularly the XPS and Precision variances, are having consistent power failures which have been associated with everything from BIOS issues to immediately following the plugging in of a USB or HDMI cable (which is my problem). I read a story of a man replacing everything in the power system until figuring out the CMOS battery was indeed the issue and after purchasing a replacement the issue finally resolved. So could it be, just maybe, that Dell has mistakenly included the ML1220 with some models just as their PDF indicates? Might they be creating failures due to the aforementioned inconsistencies of rechargeable models and only the replacement of such model with the proper CR2032 would create homeostasis within the power system? 

So again I dunno, not an electrical expert, I am just trying to figure this out like everyone else. Anybody got any insight on this? Anybody who has done the replacement care to mention which coin battery they used and does anybody recall the battery model that they replaced?

Thanks.

I replaced mine with a battery from Rome.  The replacement was the same size as the original.  The ML1220 battery is smaller than a CR2032 which has a larger diameter.  Since the Rome replacement was an exact fit, it was probably an ML1220 as the larger CR2032 would not have fit.  In this case, the spec on the Rome website stating it's CR2032 may be incorrect.  Suggest you reach out to Rome customer support to check.

@PCbluesky​  Okay thank you. Every bit of insight helps.