"What Our Gearhead® Experts Are Saying:""This battery made my Di2 upgrade seamless. It installs quickly in the seat tube, barely adds weight, and delivers all-season runtimes—huge step up from the older version.""BT-DN300 Battery is the brains behind the next generation of Shimano’s Dura-Ace and Ultegra Di2 systems, supporting advanced wireless shifting for road, gravel, and cyclocross bikes. Packed into a compact, 59g design, it mounts stealthily in the seat tube to power both front and rear derailleurs via a single, low-profile connection. The upgraded 300-series wiring boosts reliability and integrates seamlessly with Shimano’s latest wireless controls, making setup fast and essentially maintenance-free. Engineered for longevity, the BT-DN300 delivers increased charge and extended runtimes compared to previous generations, meaning more rides between plug-ins for those who train or explore year-round. The battery also features consistent voltage output—key to smooth shifting and quick response under racing or adventure conditions. Officially compatible only with the new 12-speed Di2 series, this battery is a must-have for those futureproofing a high-performance drivetrain or refreshing a modern, wireless setup."