Listening habits in a boat are much different than cars. While underway we tend to consistently play louder and also while the engine is off. Hanging out at the sand bar with music jamming, at loud volumes the average marine starting battery won't last too long. Also, once you drain a standard lead acid battery completely just a few times, it will never come back to 100% charge. It will get worse every time it's drained and recharged. We have two excellent solutions. First is adding a secondary battery. This battery is just for the stereo and other accessories. It is connected to the primary battery and alternator by a solenoid when the engine is started but when the engine is off, the secondary battery only runs the stereo and is completely isolated from the primary. Jam hard all you want and kill the secondary totally dead and the fresh primary will always start the boat. The second solution is using AGM (absorbed glass mat) batteries, at roughly the same size they provide almost twice the power. They charge full in almost half the time and most importantly they can be drained and recharged hundreds of times without problems.
Safe & Sound Mobile Electronics exclusively carries Stinger AGM batteries. There's an excellent choice for every almost every application. More power per pound and cubic inches of space used than most traditional batteries available at any price. Perfect for all automotive, marine, motorcycle and specialty applications.