Rivian Automotive is turning its worn-out EV batteries into the very power source fueling its Illinois factory. The electric-vehicle maker struck a deal with Redwood Materials to repurpose more than 100 second-life battery packs. Those packs now deliver an initial 10 megawatt-hours of dispatchable energy at the Normal, Illinois, plant. Peak grid demand? Slashed. Utility bills? Lowered. And the grid gets a breather. This setup marks the largest repurposed battery energy storage system for any U.S. automaker’s manufacturing site, according to the companies’ joint announcement. Rivian supplies the packs straight from its fleet once they’ve hit the end of vehicle life. Redwood integrates them using its Redwood Pack Manager software, which handles mixed chemistries and health states to act as one unified asset. Boom. Instant on-site power. JB Straubel, Redwood’s founder and CEO—once Tesla’s CTO—laid it out plainly.…