You are wasting your time and money with a stronger battery. Any modern car will continuously drain the battery if it is not driven. Trickle charger or battery disconnect is the answer.

In your specific scenario where you want to maintain your alarm operational but do not have electrical hook-up in your parking space, the only viable option is 2 batteries: one in he car and one in your apartment on a trickle charger and swapping them regularly.

Personally, I'd find a way to somehow run an extension chord from somewhere like an overhead lamp etc.