Dual Batteries...can 1 dead one drain the other one?

[SoldTheBayliner]

Thanks mrbobolina for the info.. that description helps. It's pretty clear that the previous owner bought 1 new battery just to sell the boat, and I didn't know any better and left the switch set to 'all', which allowed this new battery to drain while trying to feed the other (dead) battery. The new battery is charged up for the winter and is sitting in the house, and I'll get a new deep cycle (#2) battery in the spring, and make sure to flip the switch off as part of the 'home from the lake' routine. I'm optomistic that nothing on the boat is really putting a big drain on the battery when it's sitting, and it was just the one dead battery sucking the life out of the new one.

For typical (day) use, is there any reason not to just set it to 'all', so that both are getting charged when its running, and both are getting drained when stuff like the stereo is running? (assuming good batteries)?

And for a camping type situation, where I'll leave the boat in the water for 2 or 3 days, I should leave one or the other on overnight, for the just-in-case bilge situation?

[jaybird]

The simple solution is to install a charging relay and one battery will always be hot for cranking the engine. When the alternator is putting out both batteries will charge but if a power drain is on the system when the engine is off only one battery is connected to the system. This eliminates the need to remember to do anything. Many people ask why the factory does not install, more $$$$.
I would not run a 2 battery system without one. It’s such a PIA if you have to remember to turn a battery switch.
http://bluesea.com/category/78/79/pr...e/overview/329

[mrbobolina]

Thanks mrbobolina for the info.. that description helps. It's pretty clear that the previous owner bought 1 new battery just to sell the boat, and I didn't know any better and left the switch set to 'all', which allowed this new battery to drain while trying to feed the other (dead) battery. The new battery is charged up for the winter and is sitting in the house, and I'll get a new deep cycle (#2) battery in the spring, and make sure to flip the switch off as part of the 'home from the lake' routine. I'm optomistic that nothing on the boat is really putting a big drain on the battery when it's sitting, and it was just the one dead battery sucking the life out of the new one.

For typical (day) use, is there any reason not to just set it to 'all', so that both are getting charged when its running, and both are getting drained when stuff like the stereo is running? (assuming good batteries)?

And for a camping type situation, where I'll leave the boat in the water for 2 or 3 days, I should leave one or the other on overnight, for the just-in-case bilge situation?

The only reason to not leave it to all is for your alternator. Your alternator will send power that is being pulled. If your stereo is cranking hard this will drain your stereo battery. Your boat battery will be drained a little at a time. The alternator will not distinguish one from the other. So it will charge as if they are both one big ole battery. This is not a bad thing.

Where it gets more trixy is when you have alot of bass pumping. Nothing in your sound systems sucks up more than your sub(s). This will create a strong spike in draw each time the sub hits. Our stock alternators are 60 amp I think, which is reallllllllllly weak for a strong sound system. You will at some point hear your speakers start to distort, which is ghetto fabulous. When I ran a stop amp, I charged my boat battery to full, then always kept the perko on stereo. I have my jumper charged always just in case. Unless I am sitting in a cove for a long time I don't have the power challenge.

As far as the batteries that I role, I went pretty heavy. I run two Sears Die Hard Deep Cycle marine batteries. The stereo battery is a 70lb beast. I think it is the 31m. It is Blue. It is their highest cost battery. The boat battery is the 34m. I did pretty good research about which battery I wanted. I slected the 31m for a simple reason. I wanted a battery that could store along of juice. This one does. I also wanted something that could drain low and not be damaged. I run Yellow tops in my car, and they are super strong, but not good to drain down to zero as they get ruined. A deep cycle does not have this challenge.

Hope this helps.