A 48z02 is effectively a battery backed 6116 2k x8 SRAM. (No RTC, and no compatibility issues like the 48T02).
Any battery backed device with the same pinout will do the job.

The device itself probably has 26 pins with two pins emerging from the top or bottom of the device (rather than from the sides for the other 24 pins).

If you want to replace with a CR1620, CR2025, or CR2032 It's a question of exposing the pins, use a multimeter to measure the residual voltage to determine the polarity, then sever/remove the battery, solder two wires to a cell holder, then hot glue the holder to the top of the device.

My personal preference is to use a CR2032 battery - I always have them "in stock". If space is limited it's either a smaller battery or flying leads to mount the battery remotely.

Thanks for the notes.
I get that.
Looking at the datasheet recently. No pins are exposed that can be used directly or with minimal intervention. At least thats how i remember it.
My question was specifically about the physical location of the components, so the incursion on the package is minimal.

Similar modules also get used on EISA boards to retain the eisa board configurations .

I'm fairly certain I saw a video a long time ago of 'marco reps' on youtube where he replaced a similar battery backed sram module with another module that didn't need a battery.
Now if I only could remember exactly which video or what module he replaced it with... sigh.

edit: found it, though similar chip, not the same one
video : https://www.youtube.com/watch?v=upTgM_S5rAQ&t=2361s
replaced Dallas DS1230Y https://www.analog.com/en/products/ds1230y.html 256k Nonvolatile SRAM
with Ferroelectric RAM https://en.wikipedia.org/wiki/Ferroelectric_RAM - https://www.mouser.com/c/semiconductors/memor … 20type=Parallel smd ic using an adapter board to convert to DIP socket.

According to this: https://www.st.com/en/memories/m48z02.html
a Dallas/Maxim DS1220AB is pin/function replacement and obtainable thru Mouser and Digikey. The ones with + are the lead free. Look for DS1220AB+120, about $15 plus shipping....

there are fresh replacements on ebay for few bucks. almost pressed the "buy" button few times.
what stopped me was the thought that the one i have can be aigmented with external battery.
i will probably buy the replacement and then sand the old package carefully to see its internals.
this will most likely require sanding off more than needed to find out.
my question was if somebody knows of the layout already so i do the minimal change for tidy job.

thanks anyways

No have never seen one of those exact models modded or opened up.
Here is a similar DS1230 torn open: https://forum.vcfed.org/index.php?threads/rep … 9/#post-1280859

I assume you saw this eevblog forum post ? https://www.eevblog.com/forum/microcontroller … 211/#msg2639211

weedeewee wrote on 2024-05-12, 19:16:

I assume you saw this eevblog forum post ? https://www.eevblog.com/forum/microcontroller … 211/#msg2639211

🤣 - another one of my NVRAM brain dumps....

So thats you there ?
Cool.

I am actually not sure how the linked thrrad relates to the topic here.
Do you mean some of the notes how to go about "drilling" it ?

i bought a new package.
will spend time to open the lid on the one here and will post pics of the process and internals.

It was very easy to peel-off the plastic package around the battery. Used soldering iron. Expected stink, but surprisingly that was not the case.
Inside are the battery and two metal pieces connecting its poles to the EEPROM below.

A mod will be very simple.
Use a soldering iron to expose the +/- connection points on the EEPROM.
Solder wires to them. Connect a fresh battery.