Aux Battery advice

[Chrismayer]

Hi. I have a 2020 Wrangler JL and I'm a bit of a novice. I changed the main battery 2 months ago, but noticed that the stop/start still didn't work after the change. I read it may be the aux but stupidly didn't do anything about it. After a few days away over Eid, the car won't start. I've tired jumping but nothing. 

Question: Will I need to get both batteries replaced (I hope not)? and has anyone got any other idea why the jump wouldn't work? I'd prefer to get myself to a garage if I can,.