jblmk3

Good evening,
For the last couple months or so I've had issues with my battery draining in my 2020 C43. It's a 1.5 year old Mercedes battery and I've just replaced the little "Aux battery" thing under the passenger foot well. Driving the car daily, I get the battery warning after about the 3rd day or so from a full charge. And after 1-2 weeks the car won't start. I've connected a test light between the negative cable and negative battery post and unplugged every fuse I can find and nothing makes the test light go out. I've disconnected all the wires in the power distribution box that's right in front of the battery and found one that, when disconnected makes the test light go out. It's the large wire that goes into the cabin (see pics). That powers a lot of stuff I know. I'm getting intermittent bugs in the interior as well. For example, I turned off the folding side mirror option only for it to turn itself back on. The interior lights don't come on when you first open the door and several other similar oddities. I get three warning messages. Active Brake Assist Function Limited, Presafe Inoperative and Blind Spot Assist Inoperative.
Any ideas would be greatly appreciated as I'm clueless.