Traxxas recommends the high-output bec, or battery eliminator circuit, as a required accessory when installing the traxxas 2255 high-torque 400 servo in a trx-4 â® or trx-6 â® model. The traxxas high-output bec ensures maximum performance with a perfect factory fit. The kit includes everything needed to install the bec into trx-4 and trx-6 models including: bec, wire harness, and extended receiver box cover with seals