how to disable the DCM/Telematics unit in the car

Another benefit of disabling/removing DCM is you don't worry about future battery drains due to bad programming: Tell HN: 3G sunsetting is remotely killing every Subaru Outback battery | Hacker News

Idiots will come in and say "hurrrrrrrrrrrrrr that's just cause 3G was shut down, ours uses 4G". Yeah, and you never know when something will happen with the current DCM that causes it to stay awake and drain the battery. Programmers are people, and companies hire cheap programmers who don't consider all situations. Shit happens. Disabling the DCM prevents shit from happening.