Batteries

[Sanctuary 2]

Has anyone take 2 6v batteries in series (12v house) and connected them to a 12v starting battery via an battery isolation switch?

Pros?

Cons?

[ready123]

NO. Why would I want to combine deep cycle (house) with starting batteries? They are of two different types, slow discharge vs short burst high amp draw..... Neither battery type does the other's service very well. In fact by using deep cycle to supply cranking amps will shorten it's life and possibly warp the plates!
Some higher priced batteries may handle this dual service better due to their design and increased plate thickness.

What are you trying to accomplish by doing this? Is there a problem you need to solve?

Thinking out loud
I am always perplexed when I see people trying to make backup service like this..... Is something defective in their system that they have overlooked?
In the grand scheme of things a new starting battery should work flawlessly for many years starting it's engine if the system is properly maintained! If a battery is 7 years old and underperforming why hesitate to replace it......

[prowlersfish]

If your talking about using a battery Isolator to charge the house batteries and using a switch to jump them in a emergency , then its done all the time .

Now if your talking about hooking them up and using them to help start the engine all the time then no its not a good idea as Ready said .

[Sanctuary 2]

I currently have 2 group 31's on an battery isolator i plan on adding a dual bank battery charger soon.
There is no shore power on the boat. I use a shore power cable and a 115v pig tail to keep things charged.

If your talking about using a battery Isolator to charge the house batteries and using a switch to jump them in a emergency , then its done all the time .

Yes prowler that is exactly what I'm talking about. I would like a bigger house bank.
It would also leave me with an extra group 31 for something else.

Maybe i should just add a dedicated starting a battery to the above?

Or would it be better to make the 6v bank stand alone. If so how would i charge it?

Would a portable generator be a better option with my current set up?

I want to be able to spend 5 to 7 days on the hook.

Loads: 3 bilge pumps (500, 650 maybe a 1500) lights, radio, cell phones and fan.

Just kicking rocks...lol

[ready123]

I currently have 2 group 31's on an battery isolator i plan on adding a dual bank battery charger soon.
There is no shore power on the boat. I use a shore power cable and a 115v pig tail to keep things charged.
If your talking about using a battery Isolator to charge the house batteries and using a switch to jump them in a emergency , then its done all the time .
Yes prowler that is exactly what I'm talking about. I would like a bigger house bank.
It would also leave me with an extra group 31 for something else.
Maybe i should just add a dedicated starting a battery to the above?
Or would it be better to make the 6v bank stand alone. If so how would i charge it?
Would a portable generator be a better option with my current set up?
I want to be able to spend 5 to 7 days on the hook.
Loads: 3 bilge pumps (500, 650 maybe a 1500) lights, radio, cell phones and fan.
Just kicking rocks...lol

Let's do this right.
You are wanting to stay out a longtime, so either you will need to run the engine lots to charge batteries or get a generator. Not going to get into a discussion about safety concerns of using a gas powered portable on a boat.... that will take up too much space.
My earlier comment on not being suitable to charge two types as one is fitting here...... you will have an almost full starter and a low house both being fed the charging voltage.... it is much more efficient and quicker to charge each battery with a separate leg from the charger or engine while underway!
You need to give some idea of the draw of lights, radio (is there an amp), cell phones and fan....... the bilge pumps should not be working that much that we need to consider them. If they are then there are other problems requiring correction!
We need more information before getting specific....

[Sanctuary 2]

The loads above are pretty much it. Not going to use and inverter.

[ready123]

The loads above are pretty much it. Not going to use and inverter.

Then put the house on a deep cycle battery or batteries (6V) and see how it lasts say 200+ AmpHr... remember not to go below 50% which is 12.2Volts
Then once you know your usage you can decide on the charger and portable generator...... NOTE the higher the Amperage the charger the quicker it will bring your batteries back... I suggest a minimum of 50A charger. Money spent on getting a good charger is always well spent.... 50A Smart charger with at least 2 legs.