LifePO4 Battery storage voltage

I just read an article at Nordkyn Design by Eric Bretscher. Very informative. The article is about charging marine lithium battery banks and was very eye opening. My main takeaway was how I have been leaving my LifePO4 batteries stored while at the dock. I have 12volt and 24 volt systems. My house bank is 24 volt and is not being used at all while plugged into shore power. This means they can be sitting there for months not being used, or having the charger kick in at the same time daily (Float charge), creating a memory problem. Eric points out that the batteries will "degrade gradually when kept at full charge for extended periods of time and can develop memory issues when cycled inadequately". Contrary to my old way of thinking for lead acid batteries (full SOC), a low SOC is needed to preserve the LifePO4 batteries. He recommends 3.2 volts/cell, or 25.6 volts for a 24 volt battery. I was wondering if anyone else can confirm the above? I've can't find anything on my spec sheet for my batteries that refers to storage voltage. Storage temperature-yes. Voltage-no.

What you state is what I understand. In my case, my batteries are like my generator, they are at my convince and convince is more important than longevity. Therefor my batteries are always charged and ready to go.

While I charge at 14.5 I float my batteries at 13.8. Fortunately, LiPo4 batteries have gotten cheap enough that I am really not concerned with a shorter life. Unlike L-16 or 8D batteries, I can easily replace my bank by myself.

Most of the literature suggests using a float voltage (if you must) somewhat lower than LA chemistry. However the tests I have seen on storage of LFP at full vs reduced charge suggests the resultant reduction in life is modest. A lot of literature suggests fully cycling an LFP a couple of times a year to delay the dreaded dendrites.

Great points. The article does not mention how much they degrade, or how quickly they degrade (over time). As a liveaboard, it's not a hardship to turn my charger on the night before I plan on taking the boat out, so there is no reason for me to keep the batteries at full SOC.

Mac2 said:

Great points. The article does not mention how much they degrade, or how quickly they degrade (over time). As a liveaboard, it's not a hardship to turn my charger on the night before I plan on taking the boat out, so there is no reason for me to keep the batteries at full SOC.

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I don't even worry about that since my alternator will bring the batteries back to full charge before I get to any anchorage, and that's when I care about having them full.

As for voltages, 3.45 to 3.5V will charge the batteries to 99% and leave plenty of margin to avoid pushing any individual cell over 3.6V. There is very little stored energy between 3.45vpc and 3.6vpc so you are giving up almost nothing by stopping the charger a bit on the early side.

That said, some manufacturers want a higher charge voltage to run their internal balancer. But I really have to scratch my head over guidance that calls for 3.6 to 3.65vpc as a routine charge protocol. That's right at the limit of damaging the batteries.

For storage, 3.30 to 3.35 vpc is fine. I have been using 3.35 vpc for years now. When you float them at that voltage, they settle in somewhere in the 50-70% SOC range.

Mac2 said:

我刚刚在 Nordkyn Design 上读了 Eric Bretscher 的一篇文章。非常有启发性。这篇文章是关于给船用锂电池组充电的，非常令人大开眼界。我的主要收获是我在码头时一直把 LifePO4 电池存放起来。我有 12 伏和 24 伏系统。我家的电池组是 24 伏的，插入岸电时根本没用。这意味着它们可能几个月都没用，或者每天同一时间充电器启动（浮充），从而产生记忆问题。Eric 指出，电池“在长时间保持满电状态时会逐渐退化，如果循环不充分，可能会出现记忆问题”。与我以前对铅酸电池（满 SOC）的想法相反，需要低 SOC 来保护 LifePO4 电池。他建议 3.2 伏/节电池，或 24 伏电池 25.6 伏。我想知道是否还有其他人可以证实上述情况？我在电池规格表上找不到任何与存储电压相关的信息。存储温度 - 是。电压 - 否。

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Yes, lithium iron phosphate batteries are not suitable for full-charge storage. About 50% of the power is ideal. I am a professional lithium battery person.

@geoff2677
OK, you are an expert. Kindly expand on this. What is considered "storage" and then why.
When did LifePO4 (there appears to be a variety) test out to prove the suggestion.

I ask because many of us have had FLA far longer, followed the suggestions only to have them fail before the due date. Add to that the continued evolution of LFP, on what basis is this valid for ALL LFP.

My understanding and I am no expert. But researching and 2 yrs of using LifP04 on board.

I had to set my charger to bulk charge (14.1V) and a restart charge setting. (I can't think of the name of that setting but is was around 12.2V). With no float or very little float charging time. I have I have a charger/inverter and Victron charger.

Point is, To reach full charge when the batteries hit 14.1V. The charger shuts down. Then when the batteries hit 12.2V, they turn on. Now the 12.2V setting will set how much the batteries discharge, 50%, 40%.......

The settings may be different for your batteries which the specs should outline. The only problem I have, is this is going on every day. So my batteries may not be fully charged when leaving the slip. To solve this, 30 minutes before leaving. I shut the charger off and on. This makes the charger bulk charge the batteries. Problem solved.

twistedtree said:

I don't even worry about that since my alternator will bring the batteries back to full charge before I get to any anchorage, and that's when I care about having them full.

As for voltages, 3.45 to 3.5V will charge the batteries to 99% and leave plenty of margin to avoid pushing any individual cell over 3.6V. There is very little stored energy between 3.45vpc and 3.6vpc so you are giving up almost nothing by stopping the charger a bit on the early side.

That said, some manufacturers want a higher charge voltage to run their internal balancer. But I really have to scratch my head over guidance that calls for 3.6 to 3.65vpc as a routine charge protocol. That's right at the limit of damaging the batteries.

For storage, 3.30 to 3.35 vpc is fine. I have been using 3.35 vpc for years now. When you float them at that voltage, they settle in somewhere in the 50-70% SOC range.

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FWIW, Lithionics has lowered their charge recommendation to 3.6 vdc from 3.65. I've been charging at the higher rate for years and the batteries still have original capacity.

Very ture on recharging to the anchorage. I just feel better, but my Alt is a lot smaller than TT.

My Alt at 120A is doing the house, stating, and bow thruster. Also the house loads when under way.

SteveK said:

@geoff2677
OK, you are an expert. Kindly expand on this. What is considered "storage" and then why.
When did LifePO4 (there appears to be a variety) test out to prove the suggestion.

I ask because many of us have had FLA far longer, followed the suggestions only to have them fail before the due date. Add to that the continued evolution of LFP, on what basis is this valid for ALL LFP.

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Hello friend, due to my poor English, I can only use translation software to explain to you. I think your question is how to test the battery capacity and how to make your FLP battery last longer. Here are my suggestions:
1: A very important factor to consider when using LFP batteries in a country like Canada is temperature. If you use LFP in an environment of -15℃, your battery life will be affected. Since Canada is very cold in winter, I recommend placing LFP in an environment above 0℃ when not in use.
2: The battery charging current does not exceed 20% of the battery's own capacity
3: When purchasing an LPF battery pack, it is important to choose a BMS with Bluetooth function. It can better detect the health status of the battery pack for you and can repair your lithium battery pack by setting parameters.

Regarding battery capacity, the voltage platform of a single LFP cell is 3.2V, the minimum voltage is 2.65 (when in the battery), and the maximum voltage is 3.65. Assuming your LFP battery is 12V, it is composed of 4 LFP cells in series. The standard voltage of the battery pack is 12.8V, the minimum voltage is 2.65*4=10.6, and the maximum voltage is 14.6 (usually 14V or above is fully charged).

I just moved from China to Saskatoon, Canada, and I want to continue my lithium battery business there. If you have any questions about your battery, I can teach you how to test it for free. The only problem is that I don’t speak English, so it may be a bit troublesome for us to communicate. You can take pictures or videos to show me the problems you encounter, and I can understand them.

For long term storage of their LFP batteries Epoch recommends a charge of 60 to 80% then turn the battery BMS off. Following their guidelines I have stored the batteries for up to 4 months with no degradation of the SOC... For the AGMs they seem to cycle to a float charge every 4 or 5 hours

Thanks Geoff, I see a problem with translation.
These LFP batteries we have today were not around 10 years ago.
I asked how then was it determined they could not sit fully charged.
Could not be stored fully charged.

SteveK said:

谢谢 Geoff，我发现翻译有一个问题。
我们今天所拥有的这些 LFP 电池在 10 年前还不存在。
我问，那么如何确定他们不能完全充电呢？
无法在充满电的情况下保存。

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SteveK said:

谢谢 Geoff，我发现翻译有一个问题。
我们今天所拥有的这些 LFP 电池在 10 年前还不存在。
我问，那么如何确定他们不能完全充电呢？
无法在充满电的情况下保存。

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充满电后长期存放会缩短磷酸铁锂电池的寿命，一般超过6个月就会发生变化。

geoff2677 said:

充满电后长期存放会缩短磷酸铁锂电池的寿命，一般超过6个月就会发生变化。

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But HOW was that determined on a battery that has not been around as long as the expected life span. In theory? There would need to be a test side by side, same batteries for years to prove that statement. Not enough time has passed so it remains a theory

SteveK said:

But HOW was that determined on a battery that has not been around as long as the expected life span. In theory? There would need to be a test side by side, same batteries for years to prove that statement. Not enough time has passed so it remains a theory

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LFP batteries have been around for 25years with tons and tons of research. There is lots to indicate aging when held at full charge indefinitely.

twistedtree said:

LFP batteries have been around for 25years with tons and tons of research. There is lots to indicate aging when held at full charge indefinitely.

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Mostly I agree with you, this time, not. These current batteries are not or should not be the same tech. Has anyone had batteries from 25 years ago in a boat to offer an opinion. We have debated the topic wondering why all brands do not make the same claim as to expected lifespan. A poster identifies as an expert on topic, so I asked how was it determined that I will kill my batteries sooner than the expected life span. I think it is a reasonable question of an expert.

Otherwise I really do not care how long they last as long as they work as they have worked

Many large battery manufacturers are now implementing something call "Full charge protection" to ensure drop in batteries make their rated cycle count. Roypow, LiTime, Epoch and many others. It is probably assumed by these manufacturers that average users will not properly set up high quality chargers and will use basic chargers with presets. Most of these set ups with "Full Chg Protection" wont let you go over 14 to 14.2 for any length of time.

Rod Collins just celebrated his 15 years with his 400ah battery pack that he built with a capacity test that still puts out over the 400ah rated capacity. He religiously charges to 13.8 and floats at 13.5. Keep in mind even charging at 13.8 he still gets rated capacity (100%)

Here is a very good article testing charge voltages Vs time Vs capacity from 13.3 to 14.6 by Ben Stein at Panbo. The article is centered around the recent trend to lower charge voltages. I think everything Twisted Tree has stated is pretty spot on IMO. I charge to 13.9 and float at 13.5 when in use and just bump float to 13.3 for storage.

I would not be surprised that they are 25yrs old. By the time new tech is developed for the masses. Prices drop that makes seance for us common folk to buy them. Its already 4 to 8 years old.