Keeping GTC4Lusso T charged while away...

Hello all!

I recently acquired an absolutely stunning 2018 GTC4Lusso in Grigio Silverstone with tan interior thanks to another member of this forum (shout out to you Shekhar!).
I can not stop looking at it. Every time I step out of it, I walk around it admiring the shape. I have been arriving to work early which is very atypical for me because I'm so excited to drive the thing each day.
Anyway, that is not my problem. My problem is that I will be going away for 17 days and I will be leaving my baby in its parking spot at my condo. There is no outlet anywhere. I frequent this forum so I have read about the importance of keeping the car's battery topped up and the problems that can arise if you don't - and I want no part of that.
What can I use to keep the battery in good shape during that time so that when i return I won't have a dead battery and/or all those error messages? I was thinking of a power bank I can precharge and leave next to my car plugged into my car through the cable that attaches under the license plate.
When you are answering, pretend you are talking to a 5 year old. I have no understanding of electronics at all.
I also would like a solution that is fairly durable because I will have to use it again in about 6 weeks when I leave for another 2 weeks.
Thank you all iin advance for your help. I admire you all and respect the heck out of you.