From what I understand about Group...it also to do with the placement and type of the Neg and Pos connections as well as case size and tab configuration.
Top Post type, pos on right--neg left, side connectors....

For example my 1980 244 with the old style metal battery tray uses 24C---type now basically sold for older Ford farm trucks. The Poles are reversed--because the 80 batt cables have the POS near the fender----Later 240s moved the NEG cable there. The 24 also had a lip on all four sides at the bottom of the case that fits that hold down tray design. So 24 -- 24C--same bat but the C has the pole position reversed.


For the frigid north, what you want to look at is the CCA Cold Cranking Amps.
But remember you're just cranking an old tech 4 cyl engine and powering an Old tech EFI computer and fuel pump--with the oil viscosity being the main drag.

There is a newer battery tech... absorbed glass-mat (AGM) battery ...designed to meet the needs of "modern cars" meaning all the electronics that have to power up for the car to run all the sensors not to mention all that LCD screen menus stuff that has replaced switches and knobs.

Interstate Batteries---- I'm in Md but the first one I bought lasted 8 Years....replaced in 2018 and that one still fine.
The price has gone UP. I got the MT-47/H5 for $95, a the Interstate distribution warehouse---which happens to be about 5 miles from my house.
When I pulled the old battery out for them to recycle, they said wow that is an old battery....haven't seen one of those for years

Model: ___-47/H5 The MTX-47/H5 is the AGM---the most costly---$200+

https://www.interstatebatteries.com/product-search-results/1988-volvo-245-l423l.

THIS LINK MAY NOT GIVE YOU THE Info.
It May say Battery not Found and ask for you to re-enter the Make and Model and Year.

The "look for your battery' screener only goes back to 1988 for Volvo 240...but you would be entering 1989.----

The Mxx-47/H5 batteries will fit 240s all the way back when Volvo changed the Battery Tray/Hold Down design. The Screener just dosen't list it. If you enter a year earlier than 1988 the only Models that show are 740s