I have a 19' boat with a Mercruiser 4.3L V6. The altenator is a 70 amp. Currently I have one marine deep cycle battery running everything in the boat. This week I added a 10" sub powered by an amp which also powers a set of rear speakers. We do alot of tubing and boarding and the boat is running. We also anchor for 30-45 minutes at a time to swim and usually have radio on. My questions are:<br />1. What impact is the sub going to have on my battery (I am carrying a portable jump start in case I kill the battery).<br />2. If I need to add a second battery with isolator/combiner can I just run a hot wire from the accessory battery to the head unit and amp and leave everything else alone (bilge, blower, lights all run off starting battery)? There is little to no risk these items could drain battery due to low draw.<br />I am looking for a cheap solution that provides some protection.<br />Also, anyone have any idea what a stereo shop would charge to do this setup?<br />Thanks