black box on cable

This is called the intelligent battery sensor. Basically it tells the PCM and BCM what the overall state of charge the batteries are. You more then likely have the stop start system which is the engine shuts off when you come to a stop, and that means you have 2 batteries. This sensor tells the computers how much current the vehicle is using so that it can determine the overall state of charge. Once the overall state of charge drops below 75-80% the stop start system is disabled.

I attached the process on how to remove it if you ever have to because you will damage it if done wrong and then the stop start system will not work.

Let us know what questions you have. Thanks