Yes and no. Once you find a UPS with a similar voltage to the battery pack, you would have a fixed amount of time to run the unit and generate 120 V power. The reason it's better in a Prius is, the engine automatically starts as the traction battery voltage drops, providing power until you run it out of fuel... Well, there's nothing to recharge the battery pack in the Tesla... Also, I'm fairly certain Tesla would not be thrilled cycling the pack with this type of usage, I think there is even language in the warranty about not using it for this type of application.