Ideal Drop-in Lifepo4 Battery Purchase Strategy

[noelex 77]

Originally Posted by SOLAR SUPPORT

You give the example of 10A, ie 0.016C, for your batteries with a capacity of 600 Ah. The answer to your question is already in the charts. You can discharge 600Ah LA batteries up to 240/600=40% with 10A average consumption. This ratio is suitable for LA battery. If this is your situation and your batteries have not yet completed their economic life, you will continue to use them. If you replace your 600Ah LA batteries with LFP batteries, 300Ah-400Ah capacity will be enough for you.

No battery manufacturer quotes the capacity by stopping at 40% SOC. Nor do Battleborn when drawing this graph. If they did a 200Ahrs AGM battery would not measure 200Ahrs at any point of the curve.

If you want to measure battery capacity for your own use you can stop the discharge at any point,such as 40% SOC, but this is not how battery capacity is defined.

[SOLAR SUPPORT]

Originally Posted by smac999

Of course they do.

If you are 3 days from port mid winter with no sun. Abd your alternator failed. Would you rather have an 800ah agm bank at 60%. Or a 400ah lithuim bank at 20%? (Both at -300ah)

If your daily life on the boat is repeated under similar conditions, you will lose your LA batteries in a very short time. So my preference would of course be LFP.

[SOLAR SUPPORT]

Originally Posted by noelex 77

No battery manufacturer quotes the capacity by stopping at 40% SOC. Nor do Battleborn when drawing this graph. If they did a 200Ahrs AGM battery would not measure 200Ahrs at any point of the curve.

If you want to measure battery capacity for your own use you can stop the discharge at any point,such as 40% SOC, but this is not how battery capacity is defined.

For the 600AH battery group you specified, 40%Dod, which corresponds to an average consumption of 10 A, means ideal daily LA capacity usage and the discharge rate is 0.016C.

You can discharge 600 Ah battery bank with a discharge rate of 0.016C to 100% Dod and 600Ah until it reaches 10.5v. The Peukert effect will not be effective at low discharge rates. When you want to run your electric stove for one hour you need about 100A current @12V and after one hour the total capacity of your LA battery bank will drop by more than 100Ah.The Peukert number of LA batteries increases as batteries age.

The main problem is that if you discharge your LA battery to 50% or less, the service life is less than expected. In this regard, LA battery manufacturers indicate to consumers that they must comply with the 50% Dod rule in order for the battery they purchase to reach the promised number of cycles. Depending on this situation, the number of cycles committed for LA batteries is around 300-600. For LFP batteries, a lifetime of 8-10 times these cycle numbers is promised without the %Dod limitation.

[s/v Jedi]

Originally Posted by wholybee

You make a good point, there is still a lot of Wh in a LA battery at 50%. But I'm not actually sure the LA will get me home safe. Yes, the LA still has power left. But is it all USABLE? The lead acid battery drops in voltage significantly. That you still have 40%-50% of capacity left doesn't matter if your radio and Navigation equipment shuts off because the voltage is too low. With no load, a 50% LA battery is already at 12v. With even a small load, it is below 12v. Some stuff will still work. LED lights will. VHF probably will in RX mode, but in transmit might pull the voltage down too much. If you are running a laptop off an inverter for navigation? Forget it.

The reality is that in the example you gave, you probably would get the same full (meaning all your equipment works) working time out of both. Although the LA will keep the lights on after your navigation gear keeps working until it gets to 0%.

This can be resolved with a 12V to 12V dc-dc converter that can output say 13.4V regardless of input voltage being in a range like 9-16V.

[Maine Sail]

Originally Posted by SOLAR SUPPORT

For the 600AH battery group you specified, 40%Dod, which corresponds to an average consumption of 10 A, means ideal daily LA capacity usage and the discharge rate is 0.016C.

You can discharge 600 Ah battery bank with a discharge rate of 0.016C to 100% Dod and 600Ah until it reaches 10.5v. The Peukert effect will not be effective at low discharge rates. When you want to run your electric stove for one hour you need about 100A current @12V and after one hour the total capacity of your LA battery bank will drop by more than 100Ah.The Peukert number of LA batteries increases as batteries age.

The main problem is that if you discharge your LA battery to 50% or less, the service life is less than expected. In this regard, LA battery manufacturers indicate to consumers that they must comply with the 50% Dod rule in order for the battery they purchase to reach the promised number of cycles. Depending on this situation, the number of cycles committed for LA batteries is around 300-600. For LFP batteries, a lifetime of 8-10 times these cycle numbers is promised without the %Dod limitation.

Peukert works both ways. Discharges above the 20 hour rate rate reduce capacity. Discharges below the 20 hour rate yield more capacity than the 20 hour rating..

[noelex 77]

Originally Posted by SOLAR SUPPORT

The Peukert effect will not be effective at low discharge rates.

With respect, this displays a fundamental misunderstanding of the Peukert effect.

This law applies at all discharge levels.

A 600 Ahr battery measured at C20 is subject to a 30A discharge. It will have a greater capacity below this level, providing the Peuket coefficient is above one.

Battleborn make the point with their graph that a battery with a relatively high Peukert coefficient has poor performance at high rates of discharge. This is correct. This needs to be understood when discharging a battery with a high Peukert coefficient above the specified C rate.

However, they do not take into account discharge levels below the specified C rate. On most installations the battery will spend much of its time at lower C values, ie discharges less than 30A for a 600 Ahr bank. 30 A is a significant discharge for yacht house battery bank.

This is not reflected in the graph and this is why I believe it is misleading.

Lithium batteries have many real world practical advantages. Manufacturers do not need to publish misleading graphs in order sell these attributes. It is unfortunate when they resort to these tactics.

Battleborn should not be singled out. All battery manufacturers publish promotional material that is not technically accurate. AGM battery manufacturers are often worse than lithium manufacturers in stretching the truth in my view, but when advertising material is posted on Cruisers Forum the technical flaws should be pointed out.

[SOLAR SUPPORT]

Of course, it is possible to reduce the Peukert effect by creating large and heavy battery groups with LA batteries. By keeping the daily %Dod rate above 50%, it may be possible to reach the number of charge-discharge cycles promised by the manufacturer to the users.

When real life and performance considerations tell you to make a choice, it's clear what you're going to do. Calculate the usable capacity, ie the cost per AH. After all, divide the LA or LFP battery costs by the promised cycle counts and you'll be enlightened.

[Baronkrak]

Originally Posted by wholybee

But I'm not actually sure the LA will get me home safe

Normally, when the LFP load disconnect on a low cell voltage, it is the LA that get me home safely.

Originally Posted by SOLAR SUPPORT

the promised cycle counts

Yes promised.

'A bird in the hand is worth two in the bush'

[s/v Jedi]

Originally Posted by Baronkrak

Normally, when the LFP load disconnect on a low cell voltage, it is the LA that get me home safely.

Yes promised.

'A bird in the hand is worth two in the bush'

Now I get it, you are a Luddite! Is this because you actually distrust or hate the new technology or because you can’t afford it?

[Baronkrak]

Originally Posted by s/v Jedi

This can be resolved with a 12V to 12V dc-dc converter that can output say 13.4V regardless of input voltage being in a range like 9-16V.

Often required, have a dedicated communications battery, similar to the dedicated start battery.

[Baronkrak]

Originally Posted by s/v Jedi

Now I get it, you are a Luddite! Is this because you actually distrust or hate the new technology or because you can’t afford it?

Distrust.

Tesla Inc (TSLA.O) will recall more than 362,000 U.S. vehicles

[s/v Jedi]

Originally Posted by Baronkrak

Distrust.

Okay. How about the LFP batteries from the same manufacturer that made your trusted AGM batteries? In other words, is your distrust sourced in the manufacturer or in the technology itself?

[Baronkrak]

Originally Posted by s/v Jedi

Okay. How about the LFP batteries from the same manufacturer that made your trusted AGM batteries? In other words, is your distrust sourced in the manufacturer or in the technology itself?

I never purchased or installed an AGM.

Definitely the technology of lifepo4 is not “prime time"

[s/v Jedi]

Originally Posted by Baronkrak

I never purchased or installed an AGM.

Definitely the technology of lifepo4 is not “prime time"

Okay, the same manufacturer as your trusted flooded lead acid then? I mean even Trojan makes them now…

I’m not sure what you mean with “prime time”. I agree that lifepo4’s prime time may already be behind us but as technology it is fully developed and proving it’s worth every day around the world. It’s almost 30 years old technology now!

[Baronkrak]

Originally Posted by s/v Jedi

...it is fully developed and proving it’s worth every day around the world. It’s almost 30 years old technology now!

Fully developed?
Proving it’s worth?
“It’s almost 30 years old technology now!” With still plenty room for improvement.