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If you are interested in the size differences and electrical differences of lithium Iron Phosphate and Lead Acid AGM batteries,  I have started to put my battery compartment together this weekend.

I'm very interested in this. Which brand, how are they managed, what charging system you use etc. And if all that's shipping cost, you obviously bought these overseas from somewhere, not local. W

Anyone that has charges this type of chemistry through a shunt with a coulomb counter can verify these are about 99% or more efficient.    This post was not intended to be a tutorial or a

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Not to nit pick....but I can get a 200amp AGM for $335 retail....

That changes the dollar per usable for the AGMs to $5.58.......

Commercially graded AGMs have a 20 year constant use design time. "Cycles" as such,  is very hard to quantify. The actual percentage of discharge before a recharge event may be anywhere from a percentage of 1% to the full 30% (assuming that your system has a system regulator that wont allow it to discharge any further.) This of course is the same for any battery system in a boat.

High end and proper charging for LiFePo4 should have a temperature sensor on every cell , they are very sensitive to charge irregularities...

The biggest (and only ) advantage at the moment (and its a big advantage if you want to race or have a lighter displacement boat)  is the weight savings.

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12 hours ago, idlerboat said:

Commercially graded AGMs have a 20 year constant use design time.

This is misunderstood by so many. It relates to the internal connection between the plates and the ability to withstand corrosion. This is never explained by any manufacturer and the figure is very misleading. If the battery is never ever cycled, then it should last 20yrs before the internal inter-plate connections are not longer viable. The more expensive names tend to use very good corrosion resistant materials. However, cheaper manufacturers now also use similar materials and use this figure of longevity as a false positive feature in their claims. In fact I have come across several people that have thought their Battery was designed to last 20yrs when cycled. Which simply is not true. Cycle rates are still the best measure between any make of battery and the more expensive the Battery, the better that cycle number ( for same apple to apple battery type of course).

In my opinion, the best choice of Battery is the Lead Carbon design. Providing weight is not an issue. Some makes are providing cycle rates nearly as high as Li and the cheaper ones are still producing cycle rates 3 times that of standard FLA.
The problem with AGM and Gel is that you need to get a battery designed specifically for Deep cycle and that is in fact very hard to do. Most of these two, most especially the Gel types, is that they are mostly designed for Standby or UPS work. Meaning they are designed to stay trickle charged for extended periods of time without the need of equalisation charging and then be used in a deep cycle providing backup power. But their cycle rates are not so great.

Lithium batteries (of the type we would be using..there are dozens of different types) should have battery management built into the Battery itself. It should be monitoring every cell as it charges.
The issue with the Lithium batteries that have caught fire is due to a condition that the Cadnium batteries had. Filiments grow in the internals and eventually short out the cell. The poblem with the Lithium battery is that the short will then cause severe and sudden overheating and result in the thing exploding in flames. But there are now Lithium designs that are stopping this problem from occuring.

Unless weight is really important, I think it is really hard to justify the expense of LiFePo technology.

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20 hours ago, idlerboat said:

Not to nit pick....but I can get a 200amp AGM for $335 retail....

That changes the dollar per usable for the AGMs to $5.58.......

Commercially graded AGMs have a 20 year constant use design time. "Cycles" as such,  is very hard to quantify. The actual percentage of discharge before a recharge event may be anywhere from a percentage of 1% to the full 30% (assuming that your system has a system regulator that wont allow it to discharge any further.) This of course is the same for any battery system in a boat.

High end and proper charging for LiFePo4 should have a temperature sensor on every cell , they are very sensitive to charge irregularities...

The biggest (and only ) advantage at the moment (and its a big advantage if you want to race or have a lighter displacement boat)  is the weight savings.

 

LiFePo4 doesn't need temp sensors per cell.   Below 0 degree Celsius you generally should not charge them or you will risk the formation on dendrites.   You might have confussed that with AGM and other lead acid variants that should have temp compensation built in to their charging algorithms. 

Your other points are not well founded either to be honest...As there are huge charge efficiency advantages with this chemistry, it is vastly safer that flooded lead acid, Much higher discharge rates of efficiency and ability.  There are many boats now running electric galleys using these batteries and running flawlessly with solar and wind as the charge sources.  They are very light as you point out. 

 

This is a proven technology that has been used for a very long time on other fields.  It is relatively new to the boater,  so most are skeptical and have horror stories that are mostly fictional or user error based.  

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I've used a 100ah lifopo4 on a 9m racer cruiser for about 5 years now for two reasons - significant weight savings and high charge efficiency. For me, these outweigh the increased cost. While I admittedly don't have expertise on this, I'm not aware of evidence to support the fire risk concern - there is plenty of guidance out there about how safe lifepo4 technology is, and by now I think we would be hearing more lifepo4 boat fire stories if it was a risk. Will probably get flak from some for saying this....

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12 hours ago, wheels said:

In my opinion, the best choice of Battery is the Lead Carbon design. Providing weight is not an issue. 

I agree its a brilliant technology and perfect in a lot of cases  Lead carbon is very hard to go past and I was on the fence with my battery purchase between those and LiFePo4.    The biggest issue with Lead Carbon is the charge requirements of the technology are less forgiving than LiFePo4, but also they quite specialized....no issue if you have a infinitly variable controller like a Victron smartsolar for example.   However,  the voltage drop when loaded with medium to high loads in 'MY' case was not going to be acceptable.   If you are not going to run big inverters or winches or other high loads...you have the space and can handle the weight....its a no brainer get lead carbon from a reputable manufacturer at about half the price of LiFePo4.  

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The LiFePO4 "fire risk" is a non-event for boats IMHO.  Certainly in a car environment, where you have many many cells and are caning them to push some bloated passengers up a steep hill, can have issues (as in any battery technology) if a cell fails and resistance increases.  In a boat that is simply a non-starter - you only have a few cells and the load and charging amps are an order of magnitude less than the automotive stuff.  Any decent BMS will be looking at cell temperatures, in my install we have  sensors for 8 cells.

And Idlerboat - you will never get 20 years from AGMs in a cruising environment.  They like being topped up and that isn't that comment when you live on them 4/7.  I have had several people tell me their experiences with AGMs dying after 2-3 years.

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On 3/09/2020 at 8:19 PM, Dtwo said:

And Idlerboat - you will never get 20 years from AGMs in a cruising environment.  They like being topped up and that isn't that comment when you live on them 4/7.  I have had several people tell me their experiences with AGMs dying after 2-3 years.

Im not sure what that means ? AGM s do not require any physical (apart from electrical) maintenance.  They can be installed upside down quite happily.

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AGMs  wont last 20 years on a boat ?   :)  maybee... but mine are well on the way. (second hand ex critical infrastructure batteries, now on my boat for 12 years)  I guess we will have to wait for the other chemistry to get a bit older before it can make the same claims...

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