The future of the auto industry may boil down to the difference made by a single letter: R. As in, the difference between a lithium-ion battery, like those found in today’s electric vehicles made by Tesla and others, and the lithium-iron phosphate batteries coming soon to market.

As Elon Musk’s Tesla has been talking up new battery technology development as part of the lead-up to the company’s first-ever Battery Day for investors, Wall Street is buzzing about the difference the next generation of batteries may make. Vehicles with lithium-ion batteries, also used in cellphones, are expected to give way over the next few years to cars and trucks made with lithium-iron phosphate and other chemistries. This will cut costs, extend vehicle ranges to 400 miles or more between charges and enable batteries to last as long as 1 million miles.