The brain of the system. The Eps (tm) Power Unit (TM) is much more than just a battery. Its housing contains all the electronics of the Eps (tm) drivetrain, the system memory input/output gates & the battery charger plug. This design choice benefits both the reliability & the performance of the system, which is also upgradeable. Casing In Vibration Absorbent Material With Specially Contoured Interior: for maximum protection of the battery & electronic components against vibration even on very poor road surfaces Casing With Ultrasonically Welded Seams: makes the system 100% waterproof Input/output Gates for charging the battery &, when necessary, diagnosing the system & updating the firmware & Eeprom. Dti (tm) Digital Tech Intelligence: the digital brain of the Eps (tm) drivetrain. Dti monitors & checks the battery, transmits & receives signals to & from the interface & controls & monitors the functions of the rear & front derailleur. The unit also checks for system faults, warning the user when necessary via an Rgb Led