I have a Nordic Rage and currently two batteries. The stereo now is 3 larger amps and it seems that after 4-6 hours of no motor listening they will not start the boat. Should I add a third or am I just expecting to much?

Put a 3rd battery as your starting battery only. Keep it isolated from your stereo batteries. Very easy to do. Search Blue Seas Battery Relays

Yep - what he said! I did same install last summer, and it works very well.

http://www.defender.com/product3.jsp...0060&id=750169

+1. That's how mine are ran. My batteries for the stereo are Kinetik Powercells and they have performed excellent.

kinetics rock .. hc 2400 baby ,they need a hard charge though ..

I have 2 dedicated starting batteries, one for each engine, and added Blue Sea Systems battery Isolator for my 3rd Deep Cycle battery for the stereo. I’ve got six seasons out of that setup with the Deca Marine Deep cycle battery.

I used two group 31 Deka AGM deep cycle batteries wired parallel as battery #2, and battery #1 was just a standard marine starting battery. So both of the AGM batteries worked as one. This provided a solid 10 hours of 3/4 volume on a 2700 watt stereo. The alternator won't charge these monsters so I had a shore power 30amp charger hooked up to charge the "house" batteries. This was on my previous boat. I will be wiring up my new boat in the same way, except I might be adding a third group 31 to the battery bank... I will be running a rockford Fosgate Power T1500 to 2 Rockford 12s and a power t600 to 4 boston acoustic pro se60 6-3/4 components, along with 4 infinity 6x9s wired to a JL 150 watt amp...... More power, more power....

That way requires you to switch the battery switch to #2 every time you want to play your stereo and not worry about running your start battery down too though. Why not install a battery relay in your new boat to avoid remembering to always switch your battery switch from 1 to 2, and then back again, and let it keep both systems separate all the time, except when charging, all automatically?

I plan to run a 3 battery system as wel, I have a single engine, so would have 1 battery for starting and the other 2 for stereo, as my boat already has a perko switch. I planned to start on 1 then flip to both while running so all batteries charge, then when stopped switch to 2. This way if the batteries die, I still have the 1 to start the boat. How does this system work to avoid having to do that?