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bell ringer
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AGM take charge more quickly than wet.

Never require constant filling with DISTILLED water ( hidden expense and again time and effort) AGM you don't sorry about battery acid leaking.
Let first say that I don't care what type of battery people what to use on THEIR boat and don't understand why so many seem to. So many batteries choice threads are people looking to prove their decision was correct to justify whatever it was. Get the batteries you like and move along.

But far as charge acceptance
- except a fairly highly discharged battery the acceptance of AGM is not much a plus. I wonder just how often AGM owners ever put in more than 25% as current/20 hr capacity into their batteries??? I bet most don't even have a charge source that could.

water/acid
- I water my FLA batteries 1/month and it takes about 10 minutes. The 4 of them normally take about 2 cups of water. That probably works out to about $0.50/mo. I wouldn't call that "constant filling" or much of a hidden expense
- I never have ever worried about my batteries acid "leaking"

If you want to use agm, gels, lithium, or whatever batteries on YOUR boat go ahead. They are just batteries, they are met to be used, abused, and replaced when needed.
 

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hpeer-
If you are US born, the helpful folks at Social Security say that since you've made it to age 65 you will very probably live to age 86. So...you know, getting 20 years on the next set might not be such a bad idea. One less heavy thing to move around when you're 86.(VBG)

chef-
I'm an AGM fan as well, mainly because I got tired of replacing acid-eaten cloths. Factor in the cloths and maybe some carpet or other fabric, and the AGMs become cheaper than wet lead.
But I think your case of AGM vs wet lead is a bit skewed. You've gotten excellent but exceptional life from your AGMs, indicating a good charging system. Some folks have also reported 8-10 years from Rolls, Surette, and other top quality wet lead batteries. Most folks report half of that, regardless of battery type, so how you are maintaining them is more likely the reason for the great longevity.
And of course being sealed and needing no water is great--except, that gives you no ability to add water if there's been overcharging for any reason. That's a double-edged sword. The distilled water itself is trivial. 94c per gallon at WalMart, $1.50 at any supermarket in the laundry aisle if it isn't with the water products. If you need to top up frequently, that's again just a charging problem, not the battery's fault. (And how many charging systems are temperature compensated, or designed for marine use instead of cars, at all?)
In exchange for that, wet lead will be about 1/3 cheaper than AGM. Ignoring the cost of the inevitable acid eaten clothing.(G) So, not so bad for everyone, just not the right solution for all of us.
 

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So what would one recommend to replace 4-GC2 Lead Acid batteries. My batter box is built to EXACTLY fit the 4 GC2 batteries, so I’m stuck with that size format. .
If you’re happy with them, why not replace in-kind? Do you want something new?

They’re 6v, if I’m not mistaken. I suspect two 12v batts could fit where your four 6v live today. Usually that would lower your capacity, in similar footprint, but I haven’t checked dimensions. It doesn’t sound like you want to spend the money for the weight, capacity and charge advantages of lithium.

Keep in mind, if you change to anything other than flooded wet cell, you’ll need to modify all your charging systems.
 

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When we bought the boat ONE of the minor things the surveyor missed was the batteries were stuck in the bilge, not in a box, not secured in any way, and not even flat.

The bilge wasn’t working so I made a box under the nav table seat. It takes the 4 GC2 batteries arranged with one long and one short dimension on a side. It is not “tight” and there is a bit of a hole in the middle but it is a very compact arrangement. It’s a bit hard to describe the arrangement, but they do not lay side by side, or end to end. It’s not ideal, but it’s what I have.

My “charging arrangement” is two solar panels each with an MPPT controller, both panels charge the bank, a wind generator through charges the bank and has a divert load, the engine which goes through a charge isolator so it charges both the house and start batteries, and a Honda generator with a very old school heavy 12VDC charger, it puts out 50 amps and will get the batteries to about 15.5 V. The charger is not hooked up. When I want to use it, very infrequently, I clamp it onto the batteries and plug it into the generator. If it dies I’m out $150 (it’s not “Marine”, it’s not “smart”).
 

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Distilled water is not trivial outside the US. It is not only very difficult to find, it is also very expensive when you can find it. The most common form is sold in quarts at automotive and marine specialty stores as "battery water". This is yellow in color, and I can only guess it is distilled water, although it says it is "filtered for purity using state of the art equipment". Frankly, I think our watermaker probably makes this stuff in a non-yellow form.

https://www.islandwaterworld.com/battery-water-grand-prix-mi80002

Note that that is a very good price for this. I've paid $5-6 per quart in Panama and Guatemala.

While I loved our FLA banks, and think they are the best bang for the money, and that maintaining them is over-emphasized, I did find them to be a pain outside the USA. I would stock 5 gallons of distilled water when I could find it. That was 50lbs and filled the same space as the batteries themselves.

If you have new FLA's, then you won't be needing much water. As they age, they become quite thirsty. Owning older FLA's in Panama becomes a challenge at time for the silly fact of water...

Mark
 

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We just sold a nice FLA bank with an automatic watering system. For the 3 months I used it, that watering system was really nice. Definitely worth the cost if you have FLA. I balked at it in the past because it isn't too difficult to maintain FLA's, but I must admit it is ridiculously nice to just occasionally squeeze a bulb whenever you think about it and have all of the battery cells get exactly the right amount of water without ever removing the caps. Could probably even hook it up to a pump with an adjustable pressure switch to be truly automatic.

Mark
 

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bell ringer
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There ways to get pure water for a battery besides distilled. I was in water treatment and carried a bottle of ion exchange resin with me that made basically pure water from tap water
 

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Discussion Starter #109
When we bought the boat ONE of the minor things the surveyor missed was the batteries were stuck in the bilge, not in a box, not secured in any way, and not even flat.
That is one seriously incompetent surveyor! How does a surveyor miss such a serious problem? That's the kind of thing that even the volunteer "Courtesey Safety Inspectors" look at when our club does annual safety inspections!

Sent from my SM-G960W using Tapatalk
 

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That is one seriously incompetent surveyor! How does a surveyor miss such a serious problem? That's the kind of thing that even the volunteer "Courtesey Safety Inspectors" look at when our club does annual safety inspections!

Sent from my SM-G960W using Tapatalk
Well, he also missed the fact that the bilge pump (not functional), was under the muffler, which was under the drive shaft. In order to change the bilge pump you had to haul, pull he shaft, remove the muffler; THEN you could change the bilge pump.

I could go on, Ive seen a couple like this.
 

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hpeer-
Be careful with the Honda genset. Their usual "inverter" type gensets are designed for 110/120VAC output, and the 12VDC output is intended JUST for battery charging. The DC quality is incredibly ragged and can damage electronics if it is used as a DC supply directly. Somewhere on the web, there are some wonderful o'scope pictures showing this in detail.

FWIW.
 

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Best to just pretend its not there, piddling amps level anyway.

Use a quality shore charger whose max output is just under say 90% load off the main 115V output.

Ideally one that lets you derate output so can be run concurrently with other loads even when attached to a thirsty high-CAR bank when it's depleted.
 

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John,

Thanks for the warning. I’ve never used that 12vdc feature. I just use it as a source to run my charger.
 

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Anyone have experience with the Oasis Firefly batteries?
The press on them is pretty good (80-90% discharge w/o damage, quicker charging times), but I don’t know anyone who actually owns one.
I understand they’ve addressed the uneven quality issues they had several years ago although production levels lag and there’s a wait time when ordering.
 

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Yes, they live up to the hype as specialist for resisting PSOC and low-DoD abuse.

In markets where their cost is within coooeee of LFP, latter will be a better choice IMO.

Yes chronically backordered need to plan ahead, Bruce @ OceanPlanet is da man in NA, for QC commissioning and good warranty / support. I would not order direct from India.

Maine Sail has written up detailed test reports, with Nigel Calder I believe, apparently their inventor lives nearby.
 

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John, do you have personal experience with Firefly batteries? Jay said he is aware of the press on them, but didn't know anyone who actually owned them, and was seeking such experience.

Mark
 

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Mark I know you’re a Li fan still many aren’t. Take a peak at affordable cruising or look at what’s inside most cruising boats. It isn’t Li. I’m on year 6 of my lifelines. Probably put carbon in when they go. Space and weight aren’t a concern. With solar and wind getting to 100% soc isn’t as well. Cost is. Replacing/ reprogramming charging systems is.
At present with 1020 usable amp hours isn’t. Getting to run the generator with a load is.
My situation is not unusual so Li is overkill for many.
OP asked a good question. I’ve been told for a full time cruiser 8-10 years is reasonable. That’s a passed along opinion. Take it as such.
 

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Mark I know you’re a Li fan still many aren’t. Take a peak at affordable cruising or look at what’s inside most cruising boats. It isn’t Li. I’m on year 6 of my lifelines. Probably put carbon in when they go. Space and weight aren’t a concern. With solar and wind getting to 100% soc isn’t as well. Cost is. Replacing/ reprogramming charging systems is.
At present with 1020 usable amp hours isn’t. Getting to run the generator with a load is.
My situation is not unusual so Li is overkill for many.
OP asked a good question. I’ve been told for a full time cruiser 8-10 years is reasonable. That’s a passed along opinion. Take it as such.
I'm not sure why you are addressing this to me. I'm happy with whatever battery people want on their boats. As far as my posts on LFP, I was only addressing some misconceptions, and warning people about "experts" who may not actually have any real experience with them. Same for the carbon foam above.

You will pay the same for Firefly as for LFP. Programming charging sources should not be onerous. Replacing poor charging sources could be - but these types should probably be replaced for the sake of any battery chemistry health. Poor charging sources kill lead as fast as they do lithium. I can't think of a decent model of charging source - solar, wind, mains - that can't safely charge lithium. I can think of bad models that can't, and shouldn't be used with lead either.

8-10 years for a battery bank for a full-time cruiser is optimistic. That is from real experience over this time period with optimized charging, electrical, and battery maintenance systems. Gel possibly, FLA not.

As I understand it, your bank is not in use full-time, so 6yrs is not a full-use lifespan. This is not a judgement, but it is important to note. Some here have been describing the life of their battery banks, while discounting the fact that the banks are laid up half the year, and hooked to the dock doing no cycles, or shallow cycles, most of the time when they are in use. Many more years of life should be expected for these batteries over heavily used batteries of the same type - but one cannot make lifespan claims in general without noting this important point.

Most people who are heavy use and think they are getting long lifespan have over-provisioned, and not realized until the end how bad their batteries had become.

Mark
 

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Outbound, to put a finer point on my above post, please refer to post #77, where I wrote:

"If money is the sole, or overriding, consideration, then flooded golf cart batteries can't be beat. If one is not cruising or living full-time off grid, then LFP doesn't make as much sense."

Mark
 
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