 Tesla Inc boss Elon Musk urged miners to produce more nickel, a key ingredient in the batteries that power the companys electric cars, warning the current cost of batteries remained a big hurdle to the companys growth. Tesla will give you a giant contract for a long period of time if you mine nickel efficiently and in an environmentally sensitive way, Musk said on a post-earnings call on Wednesday. Nickel makes batteries energy dense so cars can run further on a single charge, and Tesla needs the metal more than ever as it looks to ramp up production of trucks and solar projects that use a lot of nickel. 