Help with adding third battery

[Jim from New York]

I could use advice don't want to blow up my boat. Is there anybody with battery experience that can lend a hand. I have to 23 foot Ventura with the 150 Honda. I'm trying to get enough battery power to run my refrigerator and lights for a day and a half on the hook without having to run the motor. I know a generator would work but I don't think thats necessary and I don't want to part with valuable storage space.

The boat has two group 24 batteries and Im hopeing to add a third. Also it has the normal off 1 2 and 1 and 2 battery switch. The 110v charger is a pronautic 1220p 3 bank charger.

What I think I know is is to hook up the second and third battery in parallel on the battery selector # 2 switch.

(What I don't know involves the 110 charger) is should I stop there or bring in the third wire from the 110 charger or just let the 2nd battery charger wire charge thought to battery 3 ?

Thanks for any help Jim

[pcg]

I'm hesitant to give electrical advice without seeing a schematic, but I can tell you that if you hook up an additional battery in parallel with your house battery, you don't need to (and shouldn't) hook up additional outputs from your charger. By adding the other battery in parallel you are essentially just adding amp-hour capacity to the existing house battery, and the rest of the electrical system cannot tell any difference.

[smckean (Tosca)]

When it comes to charging batteries, it's a good idea to remember this......

Battery health is very dependent on how batteries are charged (especially non traditional, liquid lead/acid batteries). One thing batteries need is to be fully charged at the proper voltage levels on a regular basis. Only a "smart" charger can do this; the alternator on your engine can't. So from time to time (pretty often) one needs to hook up to 120v so the charger can do its thing. That means being in a marina frequently or having a generator.

P.S. There are electronic solutions to this also that can mimic what a 120v source + charger can do. I think Victron makes such a product.

[T.R. Bauer]

It's really easy to add a battery. But with that said, if you are running a fridge, that's a ton of amps over a 36 hour period. And like others said, running the engine really won't help that much. Your fridge probably draws 3-5 amps each hour and that multiplied by 36 is 108-180 amps, which means your need about 200-360 amps of lead acid power to accomplish this feat since you can only discharge to around 50% and have lead acid batteries last very many cycles. So, depending on actual fridge draw (model # would be helpful), you are going to need 2 group 27 batteries wired in parallel for this to work - and that's if your fridge draws only 3 amps. On the top end of the scale, you are going to need 4!!!! I know yikes. You could go lithium, but they are extremely expensive and probably worth every cent in this application. How much is ice again?

[T.R. Bauer]

BTW, you're right about what you said about them both being on #2 in parallel, but if the batteries are adjacent to each other, it's easy to tie them together at that location and just have 1 wire going to the switch.

[colbysmith]

JFYI. I have two group 29 batteries in parallel for my house and one group 24 for starting. I have the refrigerator that comes in the 25, mine a 2009 year model, I assume the frig is original, and an Engle Freezer. I run both set to 3 on their rheostats, keeping the freezer around 20 degrees or less, and the frig around 40 or less. At night I have a CPap without the humidifier, and many times the anchor LED light. We may also be running a fan at night, or the Webasto heater, and an hour or two with a cabin LED light on. My Vectron shows in the upper 70 to lower 80% range after 12 hours with out the engine or generator running, or shore power. I have both the house batteries in parallel running off the same charger wire. The starting battery is on it's own charging circuit from the charger. It does take a bit longer to bring the house batteries back up then when I only had one, but that's due to the increase in AmpHours. When charging the batteries during the day while running at displacement speeds (1500 RPM), it takes 2-3 hours to bring the batteries back up to 100% showing on the Vectron battery meter.

[Jim from New York]

Thanks for all the help.
So like I was thinking just hook up to 2nd battery and forget about any wiring from the charger extra like you all agree. And also getting the 2 battery's on the same number battery switch#2 and also upgrading them to group 27 and leaving the starting battery as it is so far so good right.

So if you would please answer one more question I think ill be in good shape.
I won't have room near the area in the back where they are placed so I will be trying to bring the third one in the cabin maybe behind the refrigerator there may be room ill have to measure but in the cabin, and will get the parallel wires there paying attention to the proper gauge probably a 10 foot run of wire.

Feel free to chime in I know this is just general informational talk not to be used as any installation instructions of course

Ps if not to easy ill be getting a small geny
Jim

[journey on]

If one is to parallel two batteries, there are 2 considerations. One is that they must be the same size and the second is that they must be in the same condition. Battery characteristics change with time and being cycled so that a newer battery will try to charge the old as they run down.

For the above reasons, I run a switch between batteries, since I can switch between one and the other. My opinion, your choice.

Boris

[Jim from New York]

Thanks for all the help I see its going to work. Im guessing as Colbysmith explained I should be able to get at least 24hours running the frig and limited lighting use thats all ill need and in the cabin seems to be safe for a battery

Great helpful bunch here
Jim

[thataway]

I have over 40 years running chest type/under counter type and built in condenser, with really good insulation off 12 volts.

You have to know what your battery capacity is, and monitor it. Where you boat will determine what the refrigerator draw will be. A good rule of thumb is 60 amp hours for a single chest type refrigerator. The front opening will take a little more current, since the insulation is often not quite as good, and the number of times you open the door will also determine how much run time you will have. A refrigerator at Lake Powell, with ambient will be close to 100* during the day, will take a lot more current than a refrigerator in Maine, where the ambient is 60* during the summer. The water temperature will also be a factor.

You have group 24 batteries, and they are the minimum size for your boat and engine. They are probably of the "combination, start and "deep Cycle" which are not really deep cycle (Deep cycle will be heavier because they contain more lead.).

Many C Dorys come with Interstate dual purpose batteries so I will use them as a point of reference.
Group 24 Dual purpose has to 64 amp hours available--or 32 amp hours usable if you don't discharge more than 50% (This is a resting steady state voltage of 12.2 volts--no charging or current draw for 2 hours.)

The Group 31 Dual purpose had 100 amp hours available or 50 usable.

If you jump to Interstate's "Deep Cycle" line it is not all that much different!:
Group 24: 81 amp hours
Group 27: 88 amp hours
Group 31: 98 amp hours.

Other brands may vary slightly--up to 110 Amp hours for a group 31. The lower the current draw the more capacity...So drawing the 5 amps which is with the motor running, the standard 20 hour rating works well.

Also you have to consider the type of battery: If you are keeping the battery out of doors, then the Flooded lead acid works fine. But if you put inside the cabin they can vent hydrogen gas when charging, there is potential of both toxicity and explosion/fire. So if you want to put the battery inside the cabin--you want to go with AGM. The AGM are more expensive, should last longer and will often have a bit more capacity

You have an excellent battery charger. It is a "smart charger, and it can be profiled for various scenarios and a variety of different lead acid battery types.

For my 22's I have always gone over to 3 group 31's--and that has done well for a chest or front loading refrigerator. With the current C Dory 25, I wanted to experiment with the LiFePO4 batteries, and with two group 31, 100 amp hour batteries, I have usable 180 amp hour capacity. I can rapidly charge these batteries at 80 amps per hour--at least at the start of the charging profile--the LI batteries charge far faster. They are lighter,, resting state is 13.2 volts and maintain over 12.2 volts until 85% discharged and can be put in the cabin on almost any position (such as on the side). BUT they are expensive, need specific chargers, including a battery to battery charger from the outboard, as well as a specific profile 110 mains charger.

The flooded lead acid battery has a limited capacity to accept a charge, and will take longer to charge--ie a lower charging rate, than the AGM and LI lion type of batteries.

AGM are oK inside the cabin, they can be mounted anyway but upside down, they will charge up to 5x faster than the flooded lead acid battery. Although this is somewhat debated, a quality AGM battery will survive better after deeper discharge. With the usual recreational boater 70 or so % discharge will shorten the life, but unless you are doing this daily, it is probably not going to be significant in affecting the life span of the battery.

For your application I would go to 3 group 31 batteries. Put in a "Combiner"--Automatic charge relay or voltage sensitive realay (same thing), between the start and house bank. (The house being two group 31's in parallel. Start with new batteries of the same type and capacity. The self discharge of the AGM is minimal, They do not need electrolyte added.

As for the charger, I would put a charging lead to each battery, considering the specific charger which you have. You will not get more than 20 amps out of it total, but it will proportion if there is one battery lower than the others.

I also would put in a Victron 702 or 712--this monitors the voltage, amps used-amps in and state of charge. The 712 has more perimeters and can be read on an I phone.

[T.R. Bauer]

All good advice. Bob's way is probably the best way for full time boating and extended journeys. I don't think anyone mentioned it, but when you buy your wire to run all over the boat, if that happens, purchase marine grade wire because it has a good deal less voltage loss over a given distance and is just better wire in general. Also, when you upgrade batteries, I'd buy the biggest you have room for if you are going lead acid. And I love lead acid batteries for many things - especially the commercial 6v GC2 golf cart batteries. They are brutes that are good for many more cycles and can be discharge down way further than any of the 12v 24, 27, 29, and probably even the commercial deep cycle 31 that I'm pretty sure Bob mentioned. Before you go and buy your new batteries, look into it. I love them in my RV.

[Jim from New York]

Bob thanks for taking time to provide a thorough reply. lots of information to take in. I see there are different options to go with. Great help here I have all the info make a good decision.
Jim

[thataway]

[Baxter]

When I added ny third battery I put a Blue Sea S-1 battery combiner.
This assures that their the other batteries charged first then relay added third.
I too hesitate advice without seeing schematic.

If you go to Blue Sea web sit they will show schematic of how this works.

Last year I built a sound box for my Honda 2000 generator and have over the stern exhaust. We have c-pap breathing machines at night so we need lots of power when away from dock.

[PNW_Wesley]

This text and pictures are from my 3/13/21 post “It’s time to chill” about adding a house battery.

My goal for the electrical system was a safe and reliable system with minimal changes to the existing boat wiring. I chose to not use an automatic battery combiner scheme because I wanted more control over the system. All of the house loads are fed from the control panel.

A Renogy 100ah AGM battery and Vmax 20-amp charger are installed under the port seat, and the control panel is mounted in the port seat storage bin. A BMV-712 lets me monitor the system. I can also use my Ipad to read the BMV data.

An Acopower 120 watt foldable solar panel system can be deployed while on the hook.



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