ONE OF THE BEST PRODUCTS EVER. It has an inbuilt battery and is fully wireless so just stick it on the back of your boat and then you can control the stereo when swimming around. Available in black or white, with a diameter of just 2.5 inches and thickness of 3/8th of an inch, the Fusion MS-ARX70 ANT Wireless Stereo Remote allows you the freedom to control your audio systems from wherever is convenient on your Boat. It works up to 10m away and utilises the ANT communication protocol to enable remote user control of source, play/pause, skip and volume adjustment. It's IPX6 & IPX7 water resistant, which combined with its UV stability makes it suitable for use anywhere. It suitable for connection to a wide range of Fusion ANT enabled marine stereo systems - including the 70 Series, 755 Series, StereoActive, Apollo RA770, MS-BB100 and Panel Stereo units. It takes an easy to replace standard CR2032 cell battery.