"Why doesn't the Tesla vehicle have a 'full power down' state for storage?"
I assume this is because of the nature of Li-ion batteries. Even if you aren't pulling any current from the battery, they will still discharge over time, and eventually go through a chemical process rendering them unusable and/or dangerous. Having a "long-term storage" mode for the vehicle would only serve to make it more likely to happen by lulling owners into a false sense of security. Better to simply reinforce the need to constantly keep the vehicle in a charged-or-charging state.
I would like to understand where you get that information.
I've had a lot of experience with rechargeable batteries over the years in doing robotics, and a variety of chemical makeups. My experience is that the "self discharge" function is the result of the anions managing to convert by one means or another not related to electron injection at the anode. The mechanisms that enable this are things like electron tunneling which are probablistic, such that the discharge curve is asymptotic toward zero charge while never achieving it. That sort of discharge does not lead to the development of dendrites in the battery which would create shorts or other hazards to recharging.
My understanding is that because the Tesla has a constant drain on the battery it can drive the battery to zero.
It would be interesting to know the answer to the question can you just disconnect the battery for storage. Not willing to invest $100,000 to find out :-)
According to the GPBatteries guys LiON have no self discharge if they aren't being drawn down by a monitoring circuit. But they also mention that embedded safety circuits can run the batteries down a bit until those circuits stop working because there is insufficient charge in the battery to run them, and then the battery can't be charged (aka its a brick).
Of course you could charge it if you could get around the safety chip in that case it would just require a bit of cleverness.
Again my experience with LiON cells is that once they get to about 3V if you don't put a load on them they don't discharge any further on their own. That would seem to be supported by the chemical energy needed to absorb the anions but I am not a chemist, just an aging EE. Thanks for the links.
Here's a nice graphical rendition of what can happen. The undervoltage situations are not driven by current travelling outside the cell, they can happen even if the cell voltage drops by self-discharge.
I assume this is because of the nature of Li-ion batteries. Even if you aren't pulling any current from the battery, they will still discharge over time, and eventually go through a chemical process rendering them unusable and/or dangerous. Having a "long-term storage" mode for the vehicle would only serve to make it more likely to happen by lulling owners into a false sense of security. Better to simply reinforce the need to constantly keep the vehicle in a charged-or-charging state.