Every electronic drivetrain needs a battery, and the major players have all taken their own approaches regarding just where to put it. For EPS, Campagnolo chose to create an internally housed design to keep your battery safe and protected from the elements and your frame safe from the worst enemy of all: clutter. Since Campy slimmed down the design this year to give it greater compatibility, you'll need to use the EPS V3 Seatpost Power Unit Adapter if your frame has wider tubes. This adapter allows you to mount the battery safely and securely inside your 31. 8mm seatpost, so you can ride knowing it'll stay exactly where you need it to.