[GTALUG] war story: CMOS battery AKA Real Time Clock (RTC) battery in a notebook

[D. Hugh Redelmeier]

Almost all PCs have settings that they want to keep while the computer is 
off or even unplugged.  Ones that they don't want to keep on disk.  Things 
you set up from the firmware setup screen.

Furthermore, they have a realtime clock that runs when the machine is 
turned off or unplugged.

These are all powered by a lithium coin cell.

Eventually, that battery runs down and you have to replace it.  Five or 
ten years of lifetime seems normal.

When it runs down, the computer will forget the date, time, and all its 
setting when it is turned off.  This is annoying: every time you start up 
you have to fill in the time and other settings.

Luckily, for most computers it is easy to replace: it is in a socket in 
the motherboard.  The battery can be sourced from Dollarama or Amazon for 
a buck or two.  Just get the size right.

For (some? all?) notebooks the coin cell battery isn't used if there is a 
charge in the main battery.  So you may not notice that the coin cell 
battery is failing.

I flattened my notebook's main battery somehow (left it sleeping for a 
week?).  When I powered it on, it had no idea of the time nor what to 
boot.

Upon investigation, I find that I have to completely disassemble my 
computer to replace the battery!  They placed it on the top of the main 
board whereas access is to the bottom.  If you care, you can read page 50 
of 
<https://dl.dell.com/topicspdf/xps-15-9560-laptop_setup-guide_en-us.pdf>

It looks as if I will need some new thermal grease since I have to remove 
the heat sink from the processor.  And the coin cell assembly is not 
generic -- no Dollarama battery.
<https://www.amazon.ca/LeFix-Replacement-Battery-Connector-Precision/dp/B082G35D4R/>