Originally Posted by gregg
Dual battery systems do not have to isolated to be effective. If the system you use works, then stick with it. I, too, debated about the best way, and with 30 years experiance in the automotive repair field I know that, for example diesel trucks with a dual battery set up use no relays to seperate the batteries. What they do, that is different, and the way my batteries are connected is very simple. The positive cables to the boat are connected to the positive post of the main battery. The negative cables to the boat are connected to the negative post of the second battery. Then, the batteries are connected together in parallel. This does one very important thing. The batteries are discharged and charged evenly. The biggest enemy in a Marine battery's life, are number of cycles (discharging and recharging) and heat. When you isolate one battery and discharge it completely, it has not only been thru one deep cycle, but also creates more internal heat in the recharge process.
Diesel, I am in no way saying your system is wrong. I decided after my own experiance and research, and a pow wow with my Interstate Battery rep.(who knows batteries inside and out), that this system works the best for me. Even after a day at the beach running 2 amps, I have never had an issue. You are right about one thing, if you poop both batteries, you are screwed, so I just keep a booster pack charged and on board just in case. However, in 3 seasons with my 2002 maristar 210 have never had to use it. The other important thing for a marine battery is to keep it fully charged in the off season. When a battery becomes discharged, the acid absorbs into the plates causing sulfation, and leaves the water in a state that will freeze.
I've seen this used this way in car audio applications but never in a boat app..
The first boat stereo I did was for a very good friend of mine's grandfathers boat (his gramps has become older and isn't using it much but has a lake house) anyways, we added an isolator and a 2nd marine battery (biggest one walmart had..) I would have like to use all optima's but they just weren't in the budget.. someday maybe! Since this boat was going to be used by others and not just me and my buddy or his dad, this option was just not a viable one.. we wanted the extra off key (motor off) playing time.. and doing just 1 battery, or 2 in parallel was just not something we could do. Even in my own boat I think I would isolate them still.
I need to bring a volt meter out with me this weekend to see what kind of voltage we are getting when the boat is at full throttle.. but it works great, stereo is loud! I am hoping for around 12 volts in each battery before we start the boat.. some somewhere in the low 13's at throttle. My buddies dad did comment the boat has been running considerably better now that we have the dual batteries in.. could have been a grounding issue before, not sure.
We are adding a 12" Image Dynamics IDQ subwoofer undernear the rear seat in an enclosure we made out of 1/2 inch MDF and I am getting it line-x'd this weekend.