JAMESTOWN, Australia (Reuters) — The world’s biggest lithium ion battery, built by Tesla, was switched on to feed Australia’s shaky grid just in time for the first day of summer, meeting an ambitious promise by Tesla’s Elon Musk to build it in 100 days or give it for free. Tesla won a bid in July to build the 129-megawatt hour battery for the state of South Australia, which has expanded in wind power far quicker […]