> This is not a person trying to hook up a power source to the primary Lithium Battery, it is someone hooking up an inverter to a 12v lead acid battery that their Tesla also has.

From linked article:

> Through the low voltage architecture, you can get the power from the main battery pack and power several devices on the inverter.

I don't know how Tesla is wired but this article suggests that 12V lead acid battery is constantly charged from primary lithium battery. It sounds like hooking up electrical load to main battery but with extra steps.