12v vs. 2x6v Batteries for Sailboat

[lvictorlucas]

Since your question only "relates to charging and management of two six volt batteries" I will limit my response to the question.
1) Make sure the two 6 Volt batteries are both from the same manufacturer, model and close in serial number or date.
2) When you first install them charge them to the same voltage by connecting them in parallel before rewiring them for serial (and equalize in parallel if required depending on the type). Once a month measure the voltage across each battery and repeat if necessary. If they are not sealed measure the individual cell voltages in addition to the total battery voltages.
3) Use only distilled or deionized water if they are not sealed.
4) Keep written records of all the details including battery temperatures. These may not mean much to you unless you do a little study but will mean a lot to anyone knowledgeable of batteries.
5) If you are concerned about a shorted cell look up how to temporarily repair them on line.

[hooligan6a]

Double 6volt system is not perfect for the house bank. As I said if one battery goes out you are left with only 6 volt system. With two 12 volt batteries if one goes out you still have a 12 volt system. It happened to me in the middle of the Pacific Ocean. Result no running lights.very scary.

[john61ct]

So go for redundancy in other ways, as OP already has outlined.

The gains in having a more robust longer lasting bank are worth it.

[hooligan6a]

Originally Posted by lvictorlucas

Since your question only "relates to charging and management of two six volt batteries" I will limit my response to the question.
1) Make sure the two 6 Volt batteries are both from the same manufacturer, model and close in serial number or date.
2) When you first install them charge them to the same voltage by connecting them in parallel before rewiring them for serial (and equalize in parallel if required depending on the type). Once a month measure the voltage across each battery and repeat if necessary. If they are not sealed measure the individual cell voltages in addition to the total battery voltages.
3) Use only distilled or deionized water if they are not sealed.
4) Keep written records of all the details including battery temperatures. These may not mean much to you unless you do a little study but will mean a lot to anyone knowledgeable of batteries.
5) If you are concerned about a shorted cell look up how to temporarily repair them on line.

And all this is being done while you are underway crossing oceans? I don’t think so.

[Adelie]

I am in the same position as you with my boat, room for 2 batteries.

As such I consciously chose to go with 12v batteries so that if one dies I am still left with enough voltage to actually do things. With 2-6v batteries, if one dies you got nothing except maybe dim lights.

To that end I’m using a Trojan T-1275, 156a-h. $175 plus core charge. These are golf-cart batteries from a premium though not lux brand so I trust that they really are deep cycle.

If I couldn’t source a 12v that I trusted to be a real deep cycle I’m not sure which way I would have jumped in this.

The normal charging I have is a 30w panel that completely recharge weekend to weekend. I use a trolling motor to get in and out so discharge can be significant.

Cruising my original motor had no charging so I carried 200w of panels that I set out every day at anchor. I have replaced the motor with a new one that has charging and medium term will mount the solar panels so the produce all the time.

[Compass790]

We have 2 of 6v Crown 225 amp hr batteries & we use them for starting as well. Probably have the same starter as you Homer. They have no difficulty turning it over but ours is only an 8hp Yanmar. We do tend to spin it up using the decompression lever though as we like to get the oil pressure up before ignition Do have a spare 12v start battery but never use it
I would get a solar panel & controller as well if I was you, if you want long life on the batteries. We have a custom 50 amp alternator but only use it if it's raining for a couple of days as, like you, we don't like listening to the single Yammer banging away.
We run an Engel fridge 24/7 but get up to 10 amps out of the solar panels.

Old 6v deep cycle's chew up a lotta water as other posters say so keep an eye on that. Our alternator voltage regulator is set for 14.8v but we have a switch on the instrument panel to cut the field current if motoring a long time & batteries are full.

I will never go back to 12v batteries, the 6v deep cycle are lasting way longer

[Pete7]

Originally Posted by hooligan6a

And all this is being done while you are underway crossing oceans? I don’t think so.

My thoughts too

The OP needs a pair of batteries for very light use like us. We had a deficit of 24AH out from a bank of 160AH at breakfast this morning and I suspect his usage will be similar.

Solution as TP said earlier, stick a pair of batteries in, give a good charge on shore power and then go sailing.

People worry too much about batteries sometimes. They are expendable items, look after them as best you can but if you can't fully charge by lunchtime don't fret, it's not the end of the world

Pete

[john61ct]

Originally Posted by Adelie

To that end I’m using a Trojan T-1275, 156a-h. $175 plus core charge. These are golf-cart batteries from a premium though not lux brand so I trust that they really are deep cycle.

Yes they are an exception that proves the rule, every bit as suitable for deep cycling as their T-105 GCs, but in 12V. Maybe a bit longer lasting IRL as the EPM/Dekas.

And that's a good price if available locally.

[thomm225]

It appears you are worried a bit about having to start the engine to charge the batteries.

Did you ever consider a small solar setup?

I have two Group 27 12 Volt batteries in parallel and don't need a starter battery.

I run about the same electrical/electronics as you except I have an autopilot on while sailing and a fan (AC or DC) running all night sometimes for 12 hours. Anchor light is an LED battery powered lantern. Inverter for charging phone/laptop and to run the fan, drill, vacuum, etc

The batteries were $80.00 each or so. (90ah) You could get a PWM Solar Controller for around $35.00 and a 100 watt panel for near $100

I've also had one of my 12 volt batteries bring down my whole system and had to disconnect it and come in on just one

My system is maintained at the marina with one 65 watt panel. I have 4 panels totaling 155 watts. I add panels as needed. I have 2 PWM Controllers and one Victron MPPT Controller

The outboard doesn't have an alternator. The boat is a Bristol 27.

[_m_miles]

This was helpful to me: https://marinehowto.com/what-is-a-deep-cycle-battery/

[yalnud]

I'm buying 6- 2V batteries for my boat which will maintain my 12v system and give me 1000 amp hours. They weigh a thousand pounds though. But I'm ok with that for the extra capacity.

[spyder1100101]

Ok, I'm going to post two PDF links. one is Victrons battery balancer, they describe why you need one. the other one is a way to balance amp draw from a parallel battery bank evenly with incorrect ways to wire as well.

https://www.victronenergy.com/upload...alancer-EN.pdf

here are what your batteries are doing when they are not correctly wired.

https://www.iotaengineering.com/ppli...edcharging.pdf

[DHHerndon]

Your best bet would be to purchase two AGM batteries of the same size that you now have. AGM batteries charge faster, last much longer, and are maintenance free. Have your system rigged so that one battery operates the engine starter, and the other one serves as the house battery to operate all other electrical equipment. You should have an interconnection switch so that in emergencies, the house battery can be used to start the engine or the engine start battery can be used for the VHF radio. Also set up your system so that the engine charger (and any other charging system) charge both the starting battery and the house battery, but the draws from each battery are totally separate. There is equipment on the market from many firm that will do all of the above.

[WSMFP]

Originally Posted by john61ct

Those EPM-Deka Duracells are by far **the best** deep cycling value on the planet, especially at $160 per pair, but even at a bit over $200. Compare to Trojans, usually quite a bit higher.

Batteries +Bulbs has them for $94 after core charge. I have four of these in our boat and they've been great.

https://www.batteriesplus.com/batter...ic/na/sligc110

[drcat]

If you decide to go with just two 6v GC batteries for your house bank plus a small standby 12v starting battery, I have three suggestions
1) keep the 12v battery charged up
2) buy a boost/buck DC to DC voltage converter. They run around $16 (amazon and other places) for one that can handle 160w output, higher output ones cost a bit more. Why - if one of the two 6v battery dies you only have a 6v house bank which will not run anything. The boost voltage converter will take the 6v of the one good battery and boost it to 12v or higher and allow you to run some necessary items like nav lights, VHF, whatever up to its output capacity.
3) No matter what battery config you decide on, consider adding a small solar panel to keep batteries charged up - for around $150 you could put in a 100w flexible panel , a PMW solar charge controller, MC4 wire and 15amp output breaker/fuse. Youtube has many reviews of inexpensive panels and charge controllers.