Update on my repair:
Towed my car in on Friday with 7 miles left on the main pack and voiced my concern about the main pack being very low. I thought they were to begin work on it Friday but due to miscommunication, I hadn't authorized repair according to them. So when I authorized repair later Friday afternoon, they said they wouldn't begin work until Monday.
I received an update saying that they are working on repair and that to keep the loaner for the time being. Tuesday morning I receive a text (I believe they actually started working on it then) that they need to replace the 12V battery too. I'm pretty sure it was less than 1.5yr old battery when it was covered under warranty when I replaced it then. I tell them there were no signs the 12V battery was going prior to the MCU dying a few days before. Service advisor tells me that because the MCU was inoperative there was nothing tell it to support the 12V and says it can't be recharged. Considering the 12V message comes up in the IC rather than MCU, that's a bunch of BS and on top of that, they tell me that 12V can't be recharged (doubt they would even attempt it). I begrudgingly tell them to replace it.
Come today I get a text message an hour ago saying they finished replacing and now walking back my MCU is mine to take. They want a $500 core charge according to their shop foreman even though she had checked with a technician before and said that was fine and they were to only take the SIM card. I vehemently tell them the shop foreman is wrong and cite my consumer rights from bar.ca.gov on auto repair which I already sent them earlier when we were debating this issue. I asked if that means my MCU is covered under warranty then? I have yet to hear back. So due to negligence on their part I have to fork out an additional $212 for the 12V battery after repeatedly voicing my concern about the main pack being so low.
I also asked for my 12V battery back to see if I am able to recharge it. If they want to play that game, I am going to ask for $1000 core charge for the SIM as that should clearly belong to me. I already told them they should be able to contact AT&T or be able to disable that particular SIM by software means when I thought they wanted to take my whole Tegra board.
I don't know why this whole process feels like pulling teeth with Tesla or this particular service center.