A battery holder is configured to appropriately hold a battery unit. The battery holder includes a first holding portion that supports a first end of a battery unit while in an installed state where the battery unit is held by the battery holder. The first holding portion includes a movable member and a first biasing member. The movable member includes a first support surface that contacts the first end of the battery unit while in the installed state. The movable member is movable relative to a frame of a human-powered vehicle while in a mounted state where the battery holder is mounted to the frame of the human-powered vehicle. The first biasing member biases the movable member toward the battery unit.