I had the same with the Fiat recently. It's just under 2.5 years old but only 13,500 miles due to the Pandemic making me live like a recluse. It was starting but the instrument dials were occasionally juddering on start-up where there was insufficient battery. Dealer charged it overnight whilst in for a new aerial base in January and all was well. However a couple of weeks later after standing in the cold for a week (working from home) it was completely dead. Fiat Assistance (Allianz) came out, were very good & as he was local he leant me a spare battery as he didn't hold out any hope for mine due to the extreme cold at the time and having no need for a long journey. Went to the dealer last week and the old battery failed their test with a dead cell, so it was replaced under warranty.
I was expecting a battle as my mileage is pretty pathetic for 2.5 years and I do wonder if all the sitting around it's done during the Pandemic has done it any favours, but I don't ever use start-stop and avoid the HRW on short journeys, so I wasn't going to argue with a free battery. Good service from Allianz/Fiat Assist and the dealer though.
Definitely worthwhile that you got Alfa Assist out, Cue, as it documents the issue should you need a new battery down the line also. Interestingly when i mentioned FCA batteries the Allianz guy said FCA are the least problematic of all the brands they look after, with Volvo being the most problematic - software on the newer ones apparently. His next job was a week old one that'd broken down - always interesting to get a fairly independent viewpoint.