[aidenn0]

LiIon cells have virtually zero self-discharge. It is the battery management system that contributes nearly all of the self-discharge to a LiIon battery. You could have such a relay, but it would require some additional tools to recover from such a state (needs to get the BMS in a happy state, or the BMS itself must have the ability to charge the battery from an unknown state).

This all would seem to make sense to install though, it's far better to have a pack that needs a reset in the shop then a brick, esp. as the battery pack in the model S will make up nearly all of the resale value of the vehicle.