Replacing 12 volt House battery with four 6 volt batteries for longer off shore power

[PerfectPirate]

Originally Posted by wholybee

Why not Lithium?

Changing from 12V to 6V in series and parallel doesn't increase you capacity in the same space. Given a space, whether 12V or 6V, total capacity is the same. That is just physics, a certain amount of lead and acid will have a certain capacity, and reorganizing the cell configuration for different voltage doesn't change that. However, the 6V batteries tend to be built much better, so they are preferred.

If you're goal is to increase capacity, you really need to consider Lithium. If you are concerned about safety, cost, or complexity, educate yourself as there is a lot of misinformation.

While switching to 6V will not increase capacity given the same space, with LFP you can get 3 to 5 times the capacity, at half the weight, in the same space.

Ah for Ah, Lithium is about the same cost as a quality lead acid battery. Costs have come way down.

Warren, your response over-simplifies the issue. As the lead-acid batteries get bigger (ie. moving from Series 24 to Series 27 to Series 31 to 6-volt batteries), the power delivered per cubic inch does start to level out. However, there is a significant difference between the power density of a Series 27 vs a Series 31 (0.1313 Ah per cubic inch vs. 0.1559 Ah per cubic inch). Not so much difference between a Series 31 and a pair of 6-volt deep cycles, though (0.1559 Ah per cubic inch vs 0.1526 Ah per cubic inch). But that ignores the difference in structure and consequent chemistry. The 6-volt batteries are built with heavier lead plates that are better able to sustain power delivery as they discharge and to maintain performance over multiple discharge/recharge cycles. In terms of footprint (ie. square inches), a pair of 6-volts is far superior in power delivery even to a Series 31 (1.68 Ah per square inch vs. 1.48 Ah per square inch). All of the numbers which I used for calculations were drawn from the Rolls Batteries Catalogue, Series 4000 battery line.

Down in the USA, Lithium batteries may have been dropping in price but up here in Canada the same is not as true. A 200 Ah Lithium battery from Renogy will cost more that twice as much as a pair of Rolls 6 FS GC-HC 235 Ah lead-acid batteries, which are the best quality marine deep-cycle batteries available. Let us assume that we only want to discharge the lead-acid batteries to a 50% discharge, but we are willing to take the lithium batteries down to a 20% remaining charge (this is the recommendation of the battery makers for preserving the life of their respective batteries). Then the pair of lead-acid 6-volt batteries will deliver 0.0763 Ah per cubic inch and the lithium battery will deliver 0.095 Ah per cubic inch. In terms of footprint, the lead-acid batteries will deliver 0.84 Ah per square inch and the lithium battery will only deliver 0.8 Ah per square inch. If I am willing to sacrifice some of the lifespan of my lead-acid batteries by going beyond the 50% discharge limit, then their numbers get even better. Unless I am missing something, I am not seeing a delivery of 3 to 5 times the capacity, as you suggest. Sure, going to a pair of lithium batteries would save me about 125 pounds in weight, but since my boat already weighs 12,000 pounds that one-percent difference is not particularly significant. So, I am having trouble justifying the added cost and complications of going to lithium, at least here in Canada at the moment. In the long-term, the price-performance factors may change appreciably. In ten years or so, when my Rolls batteries finally die, who knows what the preferred battery chemistry may be?

[fxykty]

LFP batteries can be taken much lower than 20% SOC - what matters is voltage, not SOC, and the low voltage warning on my Winston LFP cells is 11.8V, approximately 4% SOC.

One of the biggest benefits is lack of voltage sag, which matters if you also want an electric galley or to run a windlass without voltage-sensitive instruments blanking out.

Another benefit is that you can run LFP batteries with a perpetual partial state of charge - it just doesn’t matter what their SOC is as long as it’s within the high-low voltage range. Most BMS like the battery to be brought up to a calculated 100% SOC monthly, but that’s only to keep the SOC and cell resistance calculations correct.

But whatever works for you, works for you. I certainly don’t care what kind of batteries anyone has.

[wadekranz]

OK so if I replace my current 12 volt acid marine battery for Lithium, what do I need to consider for my charging system and generator?

[jcapo]

Originally Posted by wadekranz

OK so if I replace my current 12 volt acid marine battery for Lithium, what do I need to consider for my charging system and generator?

There are hundreds of posts in the Lithium forum discussing that very question.

https://www.cruisersforum.com/forums/f166/

[fxykty]

Originally Posted by wadekranz

OK so if I replace my current 12 volt acid marine battery for Lithium, what do I need to consider for my charging system and generator?

Drop in LFP is relatively painless.

Two areas to check and address if needed:
- Charger should have a LFP profile and/or configuration settings that you can manual specify. Most important is stopping charging using voltage and tail current, turning off absorption, and setting float.
- Your existing alternator system determines what you would need to do. If internally regulated then charge start battery and use a DC-DC charger (with LFP setting) to charge the LFP battery. If externally regulated then could also do as above - it is the simplest solution though generally not most efficient. Alternatively, you could charge the LFP battery, but does the regulator have an LFP setting and/or configuration settings as per the charger? Also, you need to consider the battery full during extended motoring and cutting off charging without damaging the alternator.

Your generator output is likely already directed to your charger. If so, no change needed. Same for shore power.

Main battery fuse may need upgrading. And if you have a 1/2/Both/Off battery switch you’ll need to replace with a 1/2/Off switch - definitely don’t parallel LFP house and lead acid start.

[Rohan]

Originally Posted by wholybee

Why not Lithium?

Ah for Ah, Lithium is about the same cost as a quality lead acid battery. Costs have come way down.

Lithium batteries are a good deal, but the OP said he isn't an expert on power banks, and putting lithium batteries on older boats necessitates several other changes you need to make.

It would be simpler for the OP to simply add more AGM batteries than going to 6v or lithium.

Heck, for me, even installing solar for the first time was a lot easier than switching to lithium batteries.

[PerfectPirate]

Originally Posted by fxykty

LFP batteries can be taken much lower than 20% SOC - what matters is voltage, not SOC, and the low voltage warning on my Winston LFP cells is 11.8V, approximately 4% SOC.

One of the biggest benefits is lack of voltage sag, which matters if you also want an electric galley or to run a windlass without voltage-sensitive instruments blanking out.

Another benefit is that you can run LFP batteries with a perpetual partial state of charge - it just doesn’t matter what their SOC is as long as it’s within the high-low voltage range. Most BMS like the battery to be brought up to a calculated 100% SOC monthly, but that’s only to keep the SOC and cell resistance calculations correct.

Again, you have some good points. However, lead-acid can also be taken far past the point of 50% discharge. The argument that I was making is that the recommendations of the battery manufacturers to preserve battery LONGEVITY is that lithium should not go below 20% and lead-acid not go below 50%.

I do agree that lithium batteries have performance characteristics that are generally superior to lead-acid, which is why I fervently hope that their price/performance ratio gets significantly better before I finally have to replace my lead-acid batteries. Also that the safety record on lithium batteries continues to improve, especially as regards combustibility. On the other hand, 6-volt lead-acid batteries are available virtually anywhere on short notice, while getting good lithium batteries is, at the moment, much more challenging.

[Ken Goodings]

Originally Posted by fxykty

I’m glad someone pointed that out to the OP, it had me scratching my head.

We disagree.
Our 6v golfcart batteries were 230ah capacity.
The original 12 v batteries of similar size were only 170ah
They cost about $80 each in Canada and lasted 60 months in continuous tropical cruising as fulltime liveaboards.
We had six 6v batteries delivering 690ah, charged by 440w solar
So much power, we even dumped the 12v diesel starter battery!!!
A small price to pay by regular cell watering.

[EmeraldCoastSailor]

That’s what I did many years ago and have not regretted it. The wiring is simple; two pairs in serial and then the pairs connected in parallel.

[henryv]

Originally Posted by wadekranz

I don't have solar power, but I do have a generator to recharge my batteries but I don't want to have to run it as often. So this is why I am looking at longer House battery life. Currently running just my fridge off hoof lasts maybe an afternoon.

You might want to check your fridge operation. Is the compressor cycling or running continuously? It should not deplete your batteries in an afternoon.

[sinnerman]

People started using the 6 volt (golf cart) batteries in boats as they were the only sane option for getting high amp-hours from a battery specifically designed to be used as a"deep-cycle" battery.

The pros:
These batts were cheap, and readily available. (They are still readily available, but no longer that "cheap".)

You can get 225 AH from a Trojan T-105. That's a lot of juice..!

The six volt batteries are easier to lift (weight) than a comparable Amp-hour 12 volt battery.

The cons: (IMHO):
You need two batteries to make 12 volts.
Double the storage area (which in sailboats is usually hard to find)
Double the weight.

Over time the lead plates get worn thin and pieces break off (especially with vibration, banging).
This can result in a shorted cell and a dead battery.
Since you need two batteries to make 12 volts, this means the 12 volt "cell" is now out of action.

With AGM batteries,since the plates are separated by the "Absorbent glass mat" the possiblity of lead pieces shorting out the battery is significantly reduced.

Battery chargers:
And as has said, you cannot mix AGM batteries and normal lead acid battiers on the same charger (theoretically, as my boat ran like this for a while...).
The charger need to provide a three phase charging process (bulk then float),, and the periodic "equalize charge" (overvoltage) to clean up the plates.

My two cents

cheers

[Talbot]

I use 2 x 6v batteries for a total of 435 AH - these are Trojan L-16HAC. US Battery makes a similar model. Footprint is not that large, but they are tall, and weigh a LOT

[holtjp]

At this point in the evolution of battery storage systems, I can't comprehend why anyone would still be considering installing flooded lead acid batteries. If you only needed to charge a phone, run navigation lights, and power a VHF radio then FLA batteries could be the ticket. Running a fridge on anchor for even short trips requires a more substantial power storage system. Quality LFP batteries can now be purchased at a reasonable cost. They will charge quicker, weigh much less, give you far more useable capacity, and not pump dangerous gases into your boat while charging. Installation to ABYC standards is not a difficult project for a competent DIY'er.

[boatpoker]

Originally Posted by holtjp

At this point in the evolution of battery storage systems, I can't comprehend why anyone would still be considering installing flooded lead acid batteries. If you only needed to charge a phone, run navigation lights, and power a VHF radio then FLA batteries could be the ticket. Running a fridge on anchor for even short trips requires a more substantial power storage system. Quality LFP batteries can now be purchased at a reasonable cost. They will charge quicker, weigh much less, give you far more useable capacity, and not pump dangerous gases into your boat while charging. Installation to ABYC standards is not a difficult project for a competent DIY'er.

I have a few reasons to stay with lead acid ... For almost 30yrs as a full time cruiser/liveaboard and one time ABYC Certified Marine Electrician ... They are dirt cheap. I buy whatever Walmart or Costco has on sale. About 18 months ago I bought four for $100 each. I expect them to last as as long as all the other no names I've had ... about 8 years on average.

My battery compartment is properly designed and does not vent gasses into my boat. I don't need a BMS, I don't need a DC to DC converter, I don't need to modify my alternator. With our two 315W solar panels the only reason we need to got to shore is for water and diesel. We are at anchor about 7 months per year and see no reason or benefit from changing.

[Kenatsea]

Originally Posted by wadekranz

Hi, I am not a boat power expert. I want to increase my off shore power and instead of just replacing my 12 volt house battery, lads at the marina say replace with four 6 volt golf cart batteries wired in series for longer off shore power for my full sized fridge and night boat lights.
I would appreciate any advice, recommendations on type of 6 volt or is there a better 12 volt non-lithium battery in Canada I can replace old 12 volt with instead?
Any cabling tips, any DC charger changes I might have to do?

Try looking up Emily and Clarks Adventure on you-tube. Lots of great videos on power usage on boats and a ton of battery reviews. The link below is a series of tests done on all kinds of lithium batteries he has reviewed.

https://docs.google.com/spreadsheets...KeM/edit#gid=0

Good luck,