Don't know how long the batteries last, and no idea if dendrite growth is even relevant for the battery technology they are using. Tesla is giving a 1 million mile drive train guarantee and I don't know if they include the battery in that.
BUT, they are claiming total cost of ownership of $US1.26 per mile, vs $US1.51 per mile cost for an equivalent diesel - and that presumably would include any battery maintenance needed. So about a quarter of a million US dollars cheaper over a million mile lifespan.
