Electronic gears, how do they work?
There are three major component manufacturers: Shimano, SRAM, and Campagnolo. Each has their own electronic shifting system.

SRAM's is simplest to recharge: the batteries are attached directly to the front and rear derailleurs; to recharge, detach one and put it in its dedicated charging base.
Shimano has a &quot;Di2 junction box&quot; either underneath the stem or in one of the handlebar endcaps, which can be recharged with a USB cable.
Campagnolo has a system called EPS that is similar to Shimano's.