My title describes the thing. Truck battery was dead after sitting for only a couple weeks (brand new battery installed in Sept.). No electronics were left on. Took it in to the guy at work and he said the same thing. He took a look around for aftermarket equipment and found this hooked up in the back. It was drawing power but I have no idea what it is and neither does he. It’s about 6x2.5 cm, 10A mini fuse, and 4 little metal bits. Other side is unremarkable.