Second Battery

Mar 11, 2014
224
1057
In the Pimp thread Cody discusses adding a second battery. I'm starting this focused thread to get other to discuss what they have done.
My 275 came with a single battery, as I'm sure all of them did and I want to add a house battery as I just added a Fridge (See Pimp thread for where its installed).

The current switch is for a single battery, as such will need to change that out to a dual. If I understand this the the positive(red) from each battery goes to the switch. the current single battery has a yellow wire on the negative side and it seems to go somewhere in the engine compartment. I'm assuming it's grounded to the block or such...

Unlike Cody, I'm looking to add just a single dual switch so I can use either battery to run off or combine them.

Anyone have wiring/ switch recommendations? TIA
 
May 12, 2020
51
Catalina 275 Sport 31 Quincy Bay
I'm curious about this too. Blue Sea systems has an 'add-a-battery' kit that intelligently charges a starter and house battery, prioritizing the starter battery first (at least that's how I understand it). I wonder if that would work for your needs.
 
Sep 25, 2008
7,077
Alden 50 Sarasota, Florida
Depends in part on your charger - can it charge 2 batteries independently? If not, can it charge both a start and a deep cycle battery properly?
there are many ways to do what you want.
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
I'm curious about this too. Blue Sea systems has an 'add-a-battery' kit that intelligently charges a starter and house battery, prioritizing the starter battery first (at least that's how I understand it). I wonder if that would work for your needs.
One MUST understand how that system" actually works before even beginning to consider it.
Separate house batteries, switched daily for example, are not as good as a larger house bank. This has been known for decades now. Why? Lower state of discharge for any given daily load/draw.
As far as the DCP switch, please read this:
AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
Darn AGM Batteries
 
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Likes: Ward H
May 24, 2004
7,129
CC 30 South Florida
Start with what you got now, What type of battery, starter, deep cycle or dual purpose? Wet cell, AGM or Gel? What is the date of manufacture? What is the size in Amps of you engine's alternator? What type of inboard battery charger you have? What are your commonly used fixtures and appliances? What is your type of sailing, day sailor, weekender or coastal cruiser? This information would be very helpful in coming up with a recommendation.
 

F260SS

.
Oct 7, 2020
31
Catalina 275 Sport Grapevine
For my situation, day sailor, small lake, dual battery charger plugged in at the slip, I thought the Blue Sea dual circuit switch would be best. This gives me an isolated house and starting battery. I can combine for emergency starting if I need. Since I’m a belt and suspenders kind of guy I always carry a jump box with me too. My original battery failed before I installed the new switch and second battery so I went with 2 new AGM batteries. The second battery went in the port locker and it is now the starting battery. The one under the seat is the house battery. I don’t really need the engine to charge the house battery so I haven’t installed an ACR yet. I also wanted to add a few more breakers so I did a custom built pane from Blue Sea.
66BC9E7E-316D-4B39-BC2A-5578606885C2.jpeg
8118465F-36FB-4D02-B90F-1A21E9F23102.jpeg
 

Tom J

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Sep 30, 2008
2,301
Catalina 310 Quincy, MA
Unlike Cody, I'm looking to add just a single dual switch so I can use either battery to run off or combine them.
You need to clarify which switch you intend to use. It sounds like you want a 1/2/both type of switch, but you are saying "dual", which is ON/Off/Combine. Different types of circuits.
 

F260SS

.
Oct 7, 2020
31
Catalina 275 Sport Grapevine
Also, since Catalina installed the largest battery switch known to man, you will need a filler panel if you go with the Blue Sea.
 
Mar 11, 2014
224
1057
You need to clarify which switch you intend to use. It sounds like you want a 1/2/both type of switch, but you are saying "dual", which is ON/Off/Combine. Different types of circuits.
Electrical and me really don't mix. So I apologize, but now you have me more confused. Isn't the two you describe the same. That is you can use either of the two batteries or both. Naturally the Switch I'm referring to where it as a Sector for Battery one, Battery two or both also has an Off setting. What is the difference in the circuit of On off Combine. How would that off you a choice of which battery is being used?

Given Catalina has miscellaneous wires connecting to either the input or the out put of the switch and also directly to the existing I'm thinking I may be better off to simply add a second battery to increate the available amperage to the single bank I have and be done with it. Besides the Refrigerator has a voltage sensor that will ensure it turns off when the Voltage drops too far, with three levels of control for this sensor.
 

Ward H

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Nov 7, 2011
3,645
Catalina 30 Mk II Barnegat, NJ
The most common switch is the 1, 2, Both, Off switch. I believe that is what you are intending to install. It will give you a choice of using either battery for everything (house and starting) OR combine both batteries together for everything.

There is another type of battery switch called a Dual Circuit Plus. It has OFF, ON, Emergency Combine.
It isolates the two batteries from each other. This allows you to use one battery as the house battery and the other battery for another use, normally starting the engine. It prevents starting the engine from affecting the instruments causing them to shut off or reset.
It has an Emergency Combine position, which combines the two circuits.
If you don't have instrument drop out issues now with the one battery, you don't need this type of switch.

I may be better off to simply add a second battery to increate the available amperage to the single bank I have and be done with it.
Yes, that would be the simplest way to install the second battery, in parallel to your existing battery, since your goal is to increase available amperage.

If you want to use one or the other battery and sometimes both, then the 1, 2, Both, Off switch is the one you want.
 

Tom J

.
Sep 30, 2008
2,301
Catalina 310 Quincy, MA
Electrical and me really don't mix. So I apologize, but now you have me more confused. Isn't the two you describe the same. That is you can use either of the two batteries or both. Naturally the Switch I'm referring to where it as a Sector for Battery one, Battery two or both also has an Off setting. What is the difference in the circuit of On off Combine. How would that off you a choice of which battery is being used?

Given Catalina has miscellaneous wires connecting to either the input or the out put of the switch and also directly to the existing I'm thinking I may be better off to simply add a second battery to increate the available amperage to the single bank I have and be done with it. Besides the Refrigerator has a voltage sensor that will ensure it turns off when the Voltage drops too far, with three levels of control for this sensor.
My Catalina originally came with two batteries and a 1/2/both switch. Typically, I would start the engine on one battery, and let that battery charge off the alternator. At some point, I would switch to the other battery to charge it. Some battery switches allow you to switch batteries with the engine running, some don't. Look at the switch to determine which it is. The trick with this system is to remember to switch batteries. To get around this, I installed an ACR (automatic charging relay), which would switch from one battery to both when the first was fully charged.
The simplest system for you would be the second battery with the 1/2/both switch. The Blu Seas Add a Battery kit mentioned earlier in this thread would be a good choice, since it includes the ACR. You could consider using a deep cycle battery for the house bank (fridge), and a starter battery for the second battery.
You are going to have to consider cable sizes and fuses, placement, etc., so, if you aren't that friendly with electricity, study the links provided earlier here before starting. You could have a professional install the system, but you still need to know how it works before you go "out there".
 
Last edited:
May 17, 2004
5,032
Beneteau Oceanis 37 Havre de Grace
To get around this, I installed an ACR (automatic charging relay), which would switch from one battery to the other when the first was fully charged.
Just to clarify - the ACR doesn’t really switch between batteries, it just automatically combines them once the voltage on the first battery being charged reaches 13.0 Volts for 90 seconds. Since starting an engine uses very little capacity that basically means the ACR will combine the batteries shortly after the alternator starts running. I agree with your other points that it’s a very elegant solution to charge both banks without. manual switching.
 
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Likes: Tom J
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
There is another type of battery switch called a Dual Circuit Plus. It has OFF, ON, Emergency Combine.
It isolates the two batteries from each other. This allows you to use one battery as the house battery and the other battery for another use, normally starting the engine. It prevents starting the engine from affecting the instruments causing them to shut off or reset.
It has an Emergency Combine position, which combines the two circuits.
If you don't have instrument drop out issues now with the one battery, you don't need this type of switch.
Ward's right.
To learn more, read this thread:

Electrical and me really don't mix.
None of us was born an electrician. We studied it and learned. With help, like here. Good luck, all the best.
BTW, do a search here on "Electrical Systems 101" and find a link to a bunch of topics on this subject, or buy a book, Charlie Wing's is excellent.
 
Jan 17, 2022
2
columbia 8.7 edgewater
So my boat is not much bigger than yours but I am an engineer so I over do everything.
I have 2 banks (House with 4 – 6v golf cart batteries) & (starter battery – automotive type).
I have isolation switch that allows 1 (either) or both. The trick is if you isolate them when one is charging the other will not be charged.
Battery Box Circuits – Charging/Shore/Alternator/Solar



The various battery connections are documented in attachment . Full Sail has two (2) battery banks one for house power providing 470 Ah at 12V as well as a Motor Starter battery that can be isolated from the house bank to ensure the ability to start the motor regardless of the house bank. Key to shore independence is the Solar panels which are used to charge the battery, currently the panels are mounted on the coach deck and in this location their output is far less than they are capable of in the future an arch or the top of the Bimini will be provided to give them direct unshaded view of the Sun (they are able to produce up to 200 watts/hr when in direct sun view). While connected to shore power the charger will keep the batteries full, and under motor power they are constantly charged.

The various battery connections are documented above. Full Sail has two (2) battery banks one for house power providing 470 Ah at 12V as well as a Motor Starter battery that can be isolated from the house bank to ensure the ability to start the motor regardless of the house bank. Key to shore independence is the Solar panels which are used to charge the battery, currently the panels are mounted on the coach deck and in this location their output is far less than they are capable of in the future an arch or the top of the Bimini will be provided to give them direct unshaded view of the Sun (they are able to produce up to 200 watts/hr when in direct sun view). While connected to shore power the charger will keep the batteries full, and under motor power they are constantly charged.
 

Attachments

Tom J

.
Sep 30, 2008
2,301
Catalina 310 Quincy, MA
Just to clarify - the ACR doesn’t really switch between batteries, it just automatically combines them once the voltage on the first battery being charged reaches 13.0 Volts for 90 seconds. Since starting an engine uses very little capacity that basically means the ACR will combine the batteries shortly after the alternator starts running. I agree with your other points that it’s a very elegant solution to charge both banks without. manual switching.
Lol, I caught my mistake shortly after I posted it, and had already edited my post. Always good to clarify.;)