Battery replacement on start/stop

[Starjust]

Hi,
Need a bit of help..
Currently on holiday in France with my 66 plate Jetta.
Had a low battery warning on infotainment system when we disembarked from euro tunnel but made it to our hotel ok with no issues after a 90 minute drive.
2 days later without use and it was dead.
Jump started ok and after a 2 hour drive down the motorway still dead.
Made it another 3 hours after another jump start and still dead.
No warnings on dash.
After another jump, disconnected the battery and car seemed happy to keep running still (alternator ok?)
I think I've found a suitable battery replacement that I can have here in a couple of days but my manual is telling me a VW workshop needs to change the battery in a start/stop model as the electronics will need resetting....
What could I expect if I changed the battery myself?
There is a VW garage 50km away but they don't seem to have a lot of availability at the moment.
There's a garage in a neighbouring village I would like to have tried but it's shut for 2 weeks for holiday... (France eh!)

Any advice on a battery replacement in a start/stop greatly appreciated

[Crasher]

One point, NEVER run the car with the battery disconnected, the alternator will not like it. Yes a new battery needs coding in or the battery management unit (the little box on the earth lead) will tell the alternator to overcharge the new battery but you may get away with it short term.