We've discovered a new Rivian patent which reveals for the first time details on the company's Auxiliary Battery module that can increase its vehicle's range beyond the 400 mile estimate (for its top of the line models). It remains to be seen for which trims/models Rivian will offer the auxiliary battery and how much additional range the accessory will add. The battery is removable and reattachable to the vehicle, supplying power to the electric motor by being positioned in the cargo area (i.e. the cargo bed of the R1T). Once attached, the vehicle would automatically detect the battery module and make necessary adjustments according to a set of multiple predetermined features sets that determine driving performance, suspension characteristics, braking performance/sensitivity, steering ratio, etc. You can find the full patent filing below: Electric Vehicle With Modular Removable Auxiliary Battery With Integrated Cooling Abstract An electric vehicle system for transporting human passengers or cargo includes an electric vehicle that includes a body, a plurality of wheels, a cargo area, an electric motor for propelling the electric vehicle, and a primary battery for providing electrical power to the electric motor for propelling the electric vehicle. An auxiliary battery module is attachable to the electric vehicle for providing electrical power to the electric motor via a first electrical connector at the auxiliary battery module and a second electrical connector at the electric vehicle that mates with the first electrical connector. The auxiliary battery module can be positioned in the cargo area while supplying power to the electric motor, and can be removable and reattachable from the electric vehicle. The auxiliary battery module includes an integrated cooling system for cooling itself during operation of the electric vehicle including a conduit therein for circulating coolant.