Define "hold their value" You can get a three year old used Tesla for 50% off from the factory. Do a search for Tesla CPO and their site pops up.
...Their batteries have an 8 year warranty 125,000 mile warranty. if you extrapolate the Leaf's battery, you will see that they are inline.
Used Tesla's bring an equal or higher price as similarly priced luxury ICE vehicles. Considering the $7500 headwind due to the rebate, I'd say they are holding their value quite well.
You are incorrect on the warrantee terms.
All Tesla's currently offer 8 year, unlimited mileage warranties on the battery and drive train.