The SRAM battery is the power source for eTap or AXS components. The same power unit is interchangeable between front and rear eTap AXS derailleurs, Eagle AXS derailleurs, and RockShox Reverb AXS seatposts. This rechargeable battery is a great addition to your eTap AXS or Eagle AXS drivetrain, giving you 600 miles of riding per charge. It's interchangeable between front and rear derailleurs, as well as the Reverb seatpost for maximum convenience. SRAM batteries are literally a snap to remove and charge. Just flip the tool-free battery latch up and slide the battery up and out of the derailleur. Then snap the battery into the USB powered charger and connect the charger to any USB power source or A/C USB adaptor. A full charge takes up to 60 minutes to complete