Mercury - Battery Cable (30 ft) Rigging Accessory 84-8M0189596. OverviewThis 30-foot battery cable is built for boats where the battery and engine sit far apart. Instead of trying to stretch a short cable or piece together a bunch of smaller ones, this lets you run one clean line all the way through. With a proper full-length cable, your electrical system usually feels steadier-better starts, fewer power dips, and less guesswork when things get busy on the water.. Key Features • 30-Foot Length -