Ideal Drop-in Lifepo4 Battery Purchase Strategy

[noelex 77]

The graph is just advertising material produced, I presume, by Battleborn. We should be wary of accepting this type of misleading information from manufacturers.

The graph has not been drawn correctly. If both batteries were rated and performing correctly at 0.1C the capacity should be 200Ahrs not the 130Ahrs shown. At higher discharge rates lithium batteries have a capacity advantage and at lower discharge rates lead acid batteries have an avantage.

Most marine battery banks spend nearly all their time well below 0.1C. For my house battery bank 0.1C corresponds to a discharge of 60A (@24v). For the vast majority of the day my discharge rate is much lower than this and in these conditions lead acid batteries will deliver more than their 0.1C rated at capacity unlike lithium batteries where the capacity is relatively constant irrespective of the discharge rate because the Peukert's number of lithium batteries is much closer to one.

Lithium batteries do have a significant real world capacity advantage, but not because of the low Peukert's number as the graph incorrectly implies, but because in the real world the batteries can be discharged further while still providing a high cycle life.

[SOLAR SUPPORT]

Are you saying that Battleborn is publishing user-misleading information on their website?

https://en.wikipedia.org/wiki/Peukert%27s_law

[s/v Jedi]

Originally Posted by noelex 77

The graph is just advertising material produced, I presume, by Battleborn. We should be wary of accepting this type of misleading information from manufacturers.

The graph has not been drawn correctly. If both batteries were rated and performing correctly at 0.1C the capacity should be 200Ahrs not the 130Ahrs shown. At higher discharge rates lithium batteries have a capacity advantage and at lower discharge rates lead acid batteries have an avantage.

Most marine battery banks spend nearly all their time well below 0.1C. For my house battery bank 0.1C corresponds to a discharge of 60A (@24v). For the vast majority of the day my discharge rate is much lower than this and in these conditions lead acid batteries will deliver more than their 0.1C rated at capacity unlike lithium batteries where the capacity is relatively constant irrespective of the discharge rate because the Peukert's number of lithium batteries is much closer to one.

Lithium batteries do have a significant real world capacity advantage, but not because of the low Peukert's number as the graph incorrectly implies, but because in the real world the batteries can be discharged further while still providing a high cycle life.

That’s what you say… others say LA cycle life holds up even when doing more than 100% discharge!

Also, there is a flaw in your reasoning about LA having the advantage over LFP for very low loads. A load like 0.1C is completely dependent on that installed capacity. This means you need to install much more capacity to be able to get to that low figure, which completely negates that advantage. In other words: LFP can do the same with less installed capacity, both for small loads and for large loads.

[noelex 77]

Originally Posted by s/v Jedi

This means you need to install much more capacity to be able to get to that low figure, which completely negates that advantage. In other words: LFP can do the same with less installed capacity, both for small loads and for large loads.

I dont think the average boater installs more lead acid capacity to decrease the discharge rate. This is occasionally needed with drop in lithium batteries when there is a high draw device such as a bowthruster that demands more current than the otherwise desired battery bank size can deliver. This is due to limitations in the BMS. Otherwise boaters install more capacity simply because they need more capacity.

Most house discharges are well below the C10 rate. The house battery bank is usually sized to provide several days of reserve capacity at average the discharge rate. By definition the C10 rate would see the battery completely flat in only 10 hours and this is assuming it started out at 100%. SOC.

For example, take someone with a 400AHr house battery bank. The C10 discharge rate is 40A. This means if we put a constant 40A load on the battery it will deliver its rated capacity (assuming the capacity is rated at C10 and that the battery meets its specifications). At less than 40A discharge the battery capacity will be greater and at more than 40A the battery capacity will be less. Most of the time the battery bank will have a discharge significantly less than 40A, with only brief excursions above this value especially as some of the discharge will be offset by charge sources such as solar for some of the time.

I agree completely that lead acid and lithium capacity is not interchangable. Lithium capacity can be smaller, but this is not as a result of differeing Peukert's number as the Battleborn graph suggests.

[noelex 77]

Originally Posted by SOLAR SUPPORT

Are you saying that Battleborn is publishing user-misleading information on their website?

https://en.wikipedia.org/wiki/Peukert%27s_law

Battleborn are comparing a Battleborn battery with a C10 capacity of 200 Ahrs with an AGM battery that has a C10 capacity of around 130Ahr. If the manufacturer rates the battery at C20 the lead acid battery only has a capacity of around 175 Ahrs.

This is misleading in my view.

[s/v Jedi]

Originally Posted by noelex 77

I dont think the average boater installs more lead acid capacity to decrease the discharge rate. This is occasionally needed with drop in lithium batteries when there is a high draw device such as a bowthruster that demands more current than the otherwise desired battery bank size can deliver. This is due to limitations in the BMS. Otherwise boaters install more capacity simply because they need more capacity.

Most house discharges are well below the C10 rate. The house battery bank is usually sized to provide several days of reserve capacity at average the discharge rate. By definition the C10 rate would see the battery completely flat in only 10 hours and this is assuming it started out at 100%. SOC.

For example, take someone with a 400AHr house battery bank. The C10 discharge rate is 40A. This means if we put a constant 40A load on the battery it will deliver its rated capacity (assuming the capacity is rated at C10 and that the battery meets its specifications). At less than 40A discharge the battery capacity will be greater and at more than 40A the battery capacity will be less. Most of the time the battery bank will have a discharge significantly less than 40A, with only brief excursions above this value especially as some of the discharge will be offset by charge sources such as solar for some of the time.

I agree completely that lead acid and lithium capacity is not interchangable. Lithium capacity can be smaller, but this is not as a result of differeing Peukert's number as the Battleborn graph suggests.

C10 means the full discharge rate over a 10-hr period, right? Very different from a 10C rate

I thought we always use a 20hr rate and capacity number? A 400Ah battery can do 400Ah total capacity over a 20 hour period. When you discharge it over a 10-hour period, you will not reach 400Ah.

For LA people install much more capacity than they need because they want to get that small rate and shallow cycle in order to extend the battery lifetime. When they install 400Ah at 12V, they only need 200Ah and thenother 200Ah is to make the battery last longer. Except for that guy that cycles his FLA 110% daily

With LFP you can just install that 200Ah and still get thousands of cycles. People still install more capacity because they see graphs with more cycle life (i.e. 6000 cycles instead of 2000) but they forget that often their cells are refurbished and already have thousands of cycles or that the calendar lifespan is also counting and they never reach 6000 cycles in their life.

With LFP it makes sense to use capacity expressed in kWh because charge/discharge rate doesn’t affect it much. I advocate to install a LFP house battery of the capacity you need (not more) and then a year or two later install a second battery of that same capacity. Now you get ample power plus redundancy. Also, as the older battery nears end of life, you can keep using it all the way up to the day it gives up the ghost because you have that spare that is enough to keep going.

I just ordered my second battery two years after the first. The first one I built myself using 8x Winston 400Ah cells in series. It’s perfect and 10.24kWh. The second one I got two of the cheapest 24V 200Ah drop-in batteries I could find and will set them in parallel for another 10.24kWh.

The past two years I was still using an old AGM bank as 2nd battery.

I’m not really commenting on the Battleborn graph because I don’t feel like studying their documentation, but I think they are technically better than what you give them.

[SOLAR SUPPORT]

There are many websites, not just Battleborn, that compare LA and LI battery technologies. Here's another link:

https://www.victronenergy.com/blog/2...um-ion-vs-agm/

[noelex 77]

Originally Posted by SOLAR SUPPORT

There are many websites, not just Battleborn, that compare LA and LI battery technologies. Here's another link:

https://www.victronenergy.com/blog/2...um-ion-vs-agm/

The article has been written as a blog by a fellow cruiser and shows a reasonably good understanding. There are some flaws, but the biggest fault is not properly disclosing that the author is using electric propulsion on his yacht and has done so for over 9 years.

This explains his emphasis on high discharge rates. Lithium has so many advantages for electric propulsion that other battery types are not really a consideration. His conclusions are not surprising when you know this background.

Generally, before accepting as gospel the advertising and technical information from manufacturers it is better to read and understand the topic, hopefully using unbiased alternative sources. Not everything manufacturers publish should be taken at face value.

[s/v Jedi]

Originally Posted by noelex 77

The article has been written as a blog by a fellow cruiser and shows a reasonably good understanding. There are some flaws, but the biggest fault is not properly disclosing that the author is using electric propulsion on his yacht and has done so for over 9 years.

This explains his emphasis on high discharge rates. Lithium has so many advantages for electric propulsion that other battery types are not really a consideration, so his conclusions are not surprising.

Generally, before accepting as gospel the advertising and technical information from manufacturers it is better to read and understand the topic, hopefully using unbiased alternative sources.

So you agree that with LFP you only need half the Ah capacity compared to AGM? I thought the point you defended was that AGM has equal usable capacity.

Large DC loads are not just for propulsion. With more and more boats converting to all electric galleys, the large majority of LFP equipped boats now have all electric galleys and use inverter power as the energy source.

[noelex 77]

Originally Posted by s/v Jedi

I thought the point you defended was that AGM has equal usable capacity.

No, absolutely not. Sorry I did make this clear, but I did post:

Originally Posted by noelex 77

Lithium batteries do have a significant real world capacity advantage, but not because of the low Peukert's number as the graph incorrectly implies, but because in the real world the batteries can be discharged further while still providing a high cycle life.

Originally Posted by s/v Jedi

Large DC loads are not just for propulsion. With more and more boats converting to all electric galleys, the large majority of LFP equipped boats now have all electric galleys and use inverter power as the energy source.

We also currently use electric energy for all our cooking. We are almost never connected to shore power and don’t own a generator. However, I would argue that the energy required for electric cooking is quite different to the energy required for propulsion (at least for most boats). Conclusions about the ideal electrical set up for a boat using electrical propulsion are not the same as they would be for someone just requiring electric cooking. In my view, the author should have been clearer that he was considering a battery system that would be used for electric propulsion. The article and his conclusions make much more sense knowing this background.

[SOLAR SUPPORT]

Originally Posted by noelex 77

Generally, before accepting as gospel the advertising and technical information from manufacturers it is better to read and understand the topic, hopefully using unbiased alternative sources. Not everything manufacturers publish should be taken at face value.

Why should we accept your claims that the reports based on information and experiments published by brands that people, including me, are highly trusted, do not reflect the truth, and that these are publications for advertising purposes? First, please enlighten us with links to unbiased sources that confirm your claims. Are you really assuming that there is no applicable Puekert Law for LA battery chemistry? Laws are written because they reflect reality.

[noelex 77]

Originally Posted by SOLAR SUPPORT

Are you really assuming that there is no applicable Puekert Law for LA battery chemistry?

No, of course not. Peukert Law is real and the Peukert constant for lead acid batteries is higher. There are certainly times (of high discharge) when this is a drawback, but the Battleborn graph in my view has not presented the data in an accurate way, particularly at lower and more typical (for most cruisers) discharge rates.

Perhaps I can explain better using a theoretical example. Consider two batteries that are otherwise identical apart from the Peukert constant.

Battery 1) has a Peukert constant of 1.05. Battery 2) has a Peukets constant of 1.10.
Both battery banks have an identical capacity of 600Ahrs at the C20 rate.

Which battery bank will have the highest Ahr capacity with a constant 10A load?

[smac999]

Originally Posted by SOLAR SUPPORT

Your claim that "100 Ah LA and 100Ah LifePO4 batteries store the same amount of energy" is ridiculous.

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)

The agm bank is going to safely get you home. With nav lights, gps, radar etc. the lithuim bank is not.

Replacing an agm / flooded bank with a lithuim bank 1/2 the size. You lose half the battery capacity. That can be used in an emergency.

droping a flooded / agm bank to -0% and then fully recharging is not flung to hurt it. In fact sometimes it improves older banks. Annual C20 tests draining to 0 is a actually recommended as a test. And so battery monitors can be adjusted.

[wholybee]

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)

The agm bank is going to safely get you home. With nav lights, gps, radar etc. the lithuim bank is not.

Replacing an agm / flooded bank with a lithuim bank 1/2 the size. You lose half the battery capacity. That can be used in an emergency.

droping a flooded / agm bank to -0% and then fully recharging is not flung to hurt it. In fact sometimes it improves older banks. Annual C20 tests draining to 0 is a actually recommended as a test. And so battery monitors can be adjusted.

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%.

[SOLAR SUPPORT]

Originally Posted by noelex 77

No, of course not. Peukert Law is real and the Peukert constant for lead acid batteries is higher. There are certainly times (of high discharge) when this is a drawback, but the Battleborn graph in my view has not presented the data in an accurate way, particularly at lower and more typical (for most cruisers) discharge rates.

Perhaps I can explain better using a theoretical example. Consider two batteries that are otherwise identical apart from the Peukert constant.

Battery 1) has a Peukert constant of 1.05. Battery 2) has a Peukets constant of 1.10.
Both battery banks have an identical capacity of 600Ahrs at the C20 rate.

Which battery bank will have the highest Ahr capacity with a constant 10A load?

The Battleborn chart shows the results of capacity tests with current loads of 0.1-0.4C. The capacity expressions on the LA and LI batteries tested in the experiments are the same. Victron energy graphs show the results of similar tests with 0.05-5C loads.

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.