so i want to add speaker lines that would power speakers outside my boat for when im just chillin and want music, BUT i was wondering how long the battery lasts and if enyone is running 2 batteries??? any info would be great.. thanx

Depends on what amps/batts you have and how loud....I run two size 29. I have one on at the sand bar for most of the day and if needed will turn on the other if I play alot of bass. I have a 500x1 and a 300x4 jl amps

Group 29 batteries? Where did you find those? Group 27 or 31 would be more in-line with industry standards.   I run 2 optima blue tops for my stereo, powering 3 amps 4 6x9's and 2 subs. Last all day.

i have only a cd player, which runs my ipod, and 2 6'' speakers... i dont have amps or any subs...