2014 Mustang V6 Battery Drain Issues

Vehicle Info: 2014 Mustang V6 3.8 Automatic – Mustang Club of America Edition
– Mileage: 31,000
– Pony Lighting Package
– Aftermarket Powered Subwoofer Installed in Addition to Factory Stereo using Line Output Converter Wired to Rear Deck Speakers

History:
I bought this vehicle used with 14,000 miles as the second owner and it was completely stock from what I could tell. Vehicle lived most of its life in a garage before I bought it. Shortly after purchase I installed emergency lights and a siren and used them for roughly a year before removing them this week. It has had regular maintenance and no parts replaced since I’ve owned it.

The Problem:
It started the end of last winter when I noticed my battery was slow to start on cold mornings and if left to sit for more than a couple days it would have to be jumped. I got the battery tested the very next morning and it passed. The problem resolved itself when warm weather came shortly after and I had no issues until about 3-4 months ago. I don’t remember in which order the next two things happened but it was around the same time: the problem came back with my battery discharging overnight and I ran over a plastic bag and shortly after noticed a very strong plastic burning smell. I assumed the plastic got stuck to my exhaust and melted off causing the smell but got worried when the smell lasted for almost a month. I got the battery tested the very next morning it didn’t start, this time at a different place (first time a Valvoline shop, second time at Advanced Auto Parts), both times the battery passed with flying colors and the second time they also tested the charging system and it passed as well. The smell did eventually go away and so did the overnight battery drain for a while. From then on the battery drain came in spells. I’ve never been able to let the car sit for more than 2 days but as its went on It’s been more and more frequent and when I say It’s draining I mean when i get out of the car and go to lock my doors the horn won’t even give a full blow, it’s more like a muffled “pmf”, and that’s how I know I’m going to have to jump it to get it started again. At this point for 2 weeks now if I drive it for an hour or two I can let it sit for a few hours and it will start slowly, but if it does start and I only drive it for 5-10 minutes its too dead to start again as soon as I shut it off. I’ve verified the subwoofer is shutting off as it’s supposed to when the car is turned off. Another weird thing I’ve noticed is that when I go to open/close the door the window normally rolls down a tiny bit to give clearance for the door to fully shut and then rolls back up to seal. Within the past week it is no longer rolling back up when I get out of the car, as if the battery is too dead to roll it up, along with the dim lights and all other symptoms of a dead battery. Also I should add that the vehicle slowly starts right up with a jump box each time.

I really appreciate any help as I’m tight on cash and have a very busy schedule. I’m getting really tired of having to pop the hood and whip out the jump box for everything. Thanks in advance – Zach