SRAM XX1 Eagle AXS eTap Rear DerailleurWhen eTap came out, it completely revolutionized electronic shifting. You no longer needed wires in order to shift you derailleurs which created a much cleaner look that was much easier to install on any bike model. Now, this same technology is available for mountain bikes with the SRAM XX1 Eagle AXS Groupset. This new groupset brings wireless electronic shifting to the trail which enhances capability and removes complexity. SRAM's Eagle drivetrains come with a cassette that has an exceptional 10-50-tooth gear range so riding in any terrain becomes a breeze. The simplicity and efficiency of a 1x12 drivetrain provides riders an experience like never before imagined. The new AXS system connects the electronic components to your phone so you can see the battery status, change your component behavior, personalize controls, get maintenance reminders, and update the firmware. You'll be connected to your bike in a new way that was never possible before. You are currently looking at the AXS XX1 rear derailleur with a battery. If you're looking for the ultimate drivetrain for your mountain bike, then look no further than the SRAM XX1 AXS.Features12-speed drivetrain provides ultra-wide gear range allowing you to ride anywhere with easeWireless electronic shifting easily installs and provides faster, more reliable shiftingAXS system allows you to connect your drivetrain to your phone for updates, statuses, and customizationOverload Clutch protects your derailleur from incurring damage when it bangs into a rock | SRAM XX1 Eagle AXS Rear Derailleur Black, 12 Speed, AXS eTap, Battery not included