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How to Properly Charge LiFePO4 Battery?

There are still some different cautions on charge. For example, how to check if the existing lead-acid battery charger is usable? What is the most appropriate charge voltage and float voltage? How much energy do I need to keep inside the battery, and what is the best discharge end voltage? Especially in parallel, it is also important to avoid the BAD connection.

Table of Contents

If you are just looking for a simple, direct answer, please skip to the conclusion. If you want to learn more about LiFePO4 battery, or if you are a professional, please continue reading.

The Charge Voltage

The nominal voltage of one single LiFePO4 battery cell is 3.2V, and the charge voltage range is 3.50-3.65V. Note that the charge voltage cannot be higher than 3.65V, as lithium battery cells are sensitive to over voltage and over current. Please note, lithium battery has different types such as NMC, LiFePO4, and others. Here we only talk about LiFePO4 battery cells.

Over-voltage can easily cause degradation of the battery cells and performance, inflation, and even damage. So, a BMS with protection is always built-in lithium battery packs.

For the 12.8V MonoBlock Battery, the recommended charge voltage is 14.4V. If the charger’s output is not adjustable, or not that accurate, 14.0V-14.6V is acceptable.

For different voltages of LiFePO4 battery packs or systems, please refer to the following table.

Best Charge VoltageCharge Voltage Range
12V(12.8V)14.4V14.0V~14.6V
24V(25.6V)28.8V28.0V~29.2V
36V(38.4V)43.2V42.0V~43.8V
48V(15S)(48V)54.0V52.5V~54.7V
48V(16S)(51.2V)57.6V56.0V~58.4V
Charge Voltage Table of LiFePO4 Battery Packs

Unlike lead-acid batteries, they need to be fully charged every day to keep the active material from sulfation. LiFePO4 battery does not need to be fully charged, so trickle charge and float charge are not necessary.

LiFePO4 batteries only require two stages of charge, including constant current charge and constant voltage charge, which is also called bulk charge and absorption charge.

The best discharge range for LiFePO4 is 10%-90% SOC, and since the current cycle life of LiFePO4 cells reaches 6000 cycles, 5% SOC-95% is actually good enough.

Can my existing charger charge LiFePO4 batteries?

Below are a few easy steps to check if your existing charger can charge LiFePO4 batteries.

First, check if there is a repair or desulfuration function. This function generally uses a high pulse surge current.

Extreme large instant surge current will cause the LiFePO4 battery BMS to damage, or even the internal cells to inflation and damage, do not use it. Please leave it alone.

The Charger with Repair Function

Second, check if there is a battery voltage detection function.

The LiFePO4 battery’s voltage is detected as 0V after the discharge protection is triggered. So the charger will not charge this battery at all. Try to turn off this function, or change to another charger without battery voltage detection, but charge the battery directly.

Third, check the charger if it is in good condition, and insulated.

Check the manual or instructions to clarify the output voltage and max current. However, many chargers do not clearly indicate the exact output voltage, only a simple 12V or 48V, etc… In this case, we will need a voltmeter to measure it.

Charge in different scenarios

AC to DC Charger

This part is similar to the above existing chargers mentioned.

Besides of the direct battery charger, there are also chargers that connect to low-speed vehicles or machinery. Such as golf carts, sightseeing carts, patrol cars, cleaning machines, electric bikes, and other types of equipment.

There is not much difference, only the connector will be in a different standard.

A type of Golf Cart Charger

Same steps, check if there is repair or desulfuration function, check if it has battery voltage detection function, check if it is in good conditions and insulated, and check the max output voltage and current.

Solar Systems, Charge Controller

The original charge controller is similar to a lead-acid battery charger, generally designed for a 3-step charge process, constant current, constant voltage, and float charge.

LiFePO4 battery requires only 2 steps, charge voltage is recommended to be set to 14.40V (3.60V per cell).

If you have to set float voltage, please set it to 13.60V (3.40V per cell). Please refer to the table below for recommended voltages and ranges:

Best Charge VoltageFloat Charge Voltage
12V(12.8V)14.4V13.6V
24V(25.6V)28.8V27.2V
36V(38.4V)43.2V40.8V
48V(15S)(48V)54.0V51.0V
48V(16S)(51.2V)57.6V54.4V

Now a lot of people are switching old lead acid battery systems to LiFePO4 batteries.

If you are using a 12/24V battery bank, MonoBlock LiFePO4 battery can be a good option.

But if for 48V or higher solar system, it is better to choose smart batteries, such as Residential Powerwall, which can communicate with the inverter via RS485 or CAN ports.

Then the battery conditions will be monitored and optimized for a longer lifespan.

And if you are looking to build a large battery bank over 50kWh, Rack Mounted LiFePO4 battery is recommended.

Alternator to Charge

The alternator is able to charge LiFePO4 battery. But unlike lead-acid batteries, LiFePO4 battery has a very small internal resistance, which can draw too high the charge current and make the alternator overheat, smoke, and even burn.

You would need to add a DC to DC converter to limit the current.

Additionally, when a LiFePO4 battery reaches charge protection voltage, the BMS will close the circuit and creates a high voltage spike. This is also harmful to the battery.

For more details, please check out the following video from Victron:

Charge in Parallel

Take care of the charge current.

For example, if 2 units of 12.8V100Ah batteries are connected in parallel, the max charge current of one single battery is 50A.

If charging at 50A, then both the two batteries will be fully charged.

If charging at 100A, one of the batteries will be fully charged first. Then this battery will close the circuit because it reaches the charge voltage protection.

In this case, the 100A charge current will be put directly on the other circuit, which will cause the other battery to be disconnected due to charge over current. And the second battery is possibly not fully charged.

The recommended charge current should be lower than the charge limit for one single battery, i.e. 50A. In this case, even if one battery is disconnected, the other battery can continue to charge.

The same advice applies to discharge.

The BAD and BEST connections

Since the internal resistance of the LiFePO4 battery is extremely small, less than 20 mΩ, the resistance of the cables will affect the total resistance of each circuit. The higher the resistance, the lower the current.

Therefore, we need to ensure that the resistance of each individual circuit connected in parallel is similar.

  • Make sure that all cables and connectors are of the same length and size to ensure the internal connections are of the same resistance.
  • As shown in the figure, the connection shown in BAD, the positive and negative terminals of the charge side are on the same battery. This connection results in the biggest difference in circuit resistance and therefore the biggest difference in current, not recommended.

In the “Good” connection, the circuits are similar in resistance, either charge or discharge. It chooses positive and negative terminals from the different sides of the battery.

This way, each circuit goes through 3 cables with similar resistance values. The current is similar. It is recommended to use this connection for parallel connection of up to 4 batteries, more batteries in parallel will increase the current difference.

The “BETTER” connection, more complicated, basically ensures that all currents are equal. But only works for an even number of batteries connected in parallel.

The “BEST” connection, using the BUSBAR. The resistance of the BUSBAR is very small, but again, the two terminals of the CHARGE are selected with two different ends of the Busbar.

Here for the smart batteries with inter-battery communication. Even they can communicate to balance the currents, it is still better to connect with BUSBARS if several battery units are in parallel.

Charge in Series

Before connecting each battery in series, make sure the voltage difference is within 50mV, i.e. 0.05V.

One of the batteries in a series circuit will cut off the entire circuit when it reaches the protection voltage, so it is important to equalize the batteries.

Regular balancing between batteries is important. Just like lead-acid batteries, balancing enables the batteries to work at better performance and longer lifetime. It is recommended to do the balance once in a few months.

Battery Meter

Battery meters can directly display the battery voltage, current, SOC, and other status. So that you can know the battery working conditions directly.

External Battery Meter and internal Battery Meter

Some batteries are built with internal current detection devices and the figures can be output to an external LCD.

For those batteries without an internal current sampler, an external battery meter is also an option.

The difference between current meter and voltage meter

The voltage-based battery meter does not really work for LiFePO4 batteries, because its discharge curve is too flat, at 3.2V/Cell most of the time.

Current and time-based battery meters can accurately calculate the amount of energy discharged and charged. As long as the benchmark is set, the SOC display will be accurate.

Charge below 0℃

Self-heating battery is heating up the cell pack with the internal heating film, making it reach above 5℃. Then it will be good for charging.

Generally, the energy source required to heat the battery is set to be from the charge current. For some special applications, it can also be set to be from the battery.

LiFePO4 Battery Storage

It is best to store LiFePO4 battery at around 50% SOC. If there is a battery switch, it is recommended to turn off the charge/discharge switch to avoid accidental short circuit.

Conclusion

  • * For 12V(12.8V) LiFePO4 battery, the recommended charge voltage is 14.4V, 14.0~14.6V charger is also accepted. 24V, 36V, 48V batteries or systems are multiplied by 2,3,4 times. That is 28.8V(28.0V~29.2V), 43.2V(42.0V~43.8V), 57.6V(56.0V~58.4V).
  • * For existing chargers, check whether there is a repair (desulfuration) function, check whether there is a battery voltage detection function, if either is available, it can NOT  be used.
  • Check if the existing charger is in good condition and insulated, check the max output voltage and current, and if they are within the recommended and allowed range of the battery, it is OK to use.
  • * If connected in parallel, ensure that all internal cables and connectors are the same and avoid “BAD” connection.
  • * If connected in series, it is quite important to keep the batteries balanced.
Andy
Andy
Hi, I’m Andy. Since the year 2015, I’ve been working in SunOn Battery, a manufacturer in China that makes various batteries for 15 years now. The purpose of this article is to share with you the knowledge related to batteries and energy storage solutions from a Chinese supplier’s perspective.

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40 Responses

  1. Hello Andy!

    An advice please!
    If I have a LFP of ~12V 6Ah, can I charge it with 0.3A without problems?

    The same battery bellow zero degrees, has to be heated, but I think 0.3A will not be enough, right?

    1. Hi Vio,

      0.3A to 6Ah is only 0.05C, it is totally fine to charge the battery.

      If below 0 ℃, the current may be enough to heat it up, depending on how much low the temperature is.

      Andy

  2. Hi Andy
    How do i set a charge level of max 90% in reality? E.g. victron 75/15 or similar dont support this as far as i understand. Lowering the charge voltage seems not to be the right way as mentioned here:
    https://community.victronenergy.com/idea/149175/configurable-maximum-soc-in-dvccess-controled-syst.html
    https://community.victronenergy.com/questions/151813/max-soc-limit-setting-in-ess-is-very-necessary.html
    I honestly dont find any useful information on this after hours of searching. I mean so many battery providers mention higher cycles at DoD 80%, as well as in many articles, but so far no hint on how this will be setup in practice. Can you help me here pleaseplease?!

    1. Hi Kevin,

      If the inverter or charge controller doesn’t have this SOC limit function, then charge voltage can help.
      Charge voltage at around 3.50 per cell, for example, 56.0V for 51.2V battery pack. It will be charged to around 90%, but not that accurate.

      The recommended charge voltage is 3.60V per cell and 57.6V for 51.2V battery packs.
      The key point is, it is not necessary to charge the battery to 100% full.

      In theory, 10% to 90% is the best range of LiFePO4 battery.
      But in my mind, 5% to 95% is already good enough.
      Anyway, if you really want to set a 90% SOC limit, I think you can find a proper charge voltage.

      Wish it answers your question.

      Andy

  3. Hello Andy!

    If I have a LFP of ~12V 10Ah, can I charge it with 5A without problems?
    I want to know how many volt and currents would be perfect for this.

    1. Hello Opi,

      5A will be fine for most conditions, it is 0.5C for your 12V10Ah battery.
      But you will also need to check your BMS settings about the max current.

      If your nominal voltage is 12.8V, with 4 cells in series, the recommended charge voltage is 14.4V.

      Andy

  4. Hi Andy …

    I do having battery pack which is 24V/400Ah LIFEPO4 8 cell system. But each cell voltages bit difference and as below. Cell 1 = 3.362 ,Cell 2 = 3.385 ,Cell 3 = 3.402 ,Cell 4 = 3.357 ,Cell 5= 3.404 ,Cell 6= 3.354 ,Cell 7 = 3.402 , & Cell 8 = 3.404.

    Charging parameters left at inverter as 01. Bulk Charging voltage = 28.4V 02. Floating Charge voltage = 27.2V, Maximum Total Charge current = 40A, Maximum Utility charge current = 10A. (Battery gets charge va inverter only utility and no PV connected)

    Please help me how to get equalize my cells.

    Battery Pack Details

    Voltage & Capacity
    01. Nominal Voltage = 25.6V
    02. Nominal Capacity = 400Ah
    03. Nominal Energy = 10240Wh

    Discharge & Charge
    01. Max. Cont. Discharge Current = 100A
    02. End of Discharge Voltage = 20V
    03. Maximum charge Voltage = 29.2V
    04. Maximum charge current = 50A
    05. Charge method = CC/CV

    PRODUCT NAME = TAICO
    Shenzhen Taico Technology Co., Ltd.
    Contact name:
    Melody Zhu
    Registered company address:

    CN,Guangdong,Shenzhen,1035, 1036, 1038 Dongming Building, Minkang Road, Zhangkeng Community, Minzhi Street
    Company tel:
    85-0755-29822748
    Company email:
    taico1036@aliyun.com

    THEY NOT HELPING ME TO RECTYFY ISSUE. STILL BATTERY UNDER WARRENTY.

    1. Hi Rohitha,

      To balance the cells in a pack, the first way is to charge the battery cell one by one. Charge the 1st cell separately to 3.60 or even 3.65V, then the next one.

      The second way is, charge the whole pack at voltage of 28.0V, making sure there is no cell reaching the over-voltage protection.
      Hold at this charge state with very little current such as 100mA, the BMS balance function will make it balance at 3.5V.
      If there one cell reaches the voltage limit, lower the charge voltage.

      After that, if you want the cells to balance at 3.60V, raise the voltage to 28.8V with very little current.

      Both methods require tools, if it does not affect much on your use, the balancing is not quite necessary.
      The BMS balance function will make the cells rebalanced again after a few weeks.

      Andy

      1. Hi Andy …

        Many thanks to reply above.
        I’m charging my above LFEPO4 (24V/400Ah) battery pack using inverter. the battery charging settings of inverter left as follow…

        1 Maximum Utility charge current – 10A
        2 Battery equalization voltage – kept Disable
        3 Bulk Charging voltage – 28.8V
        4 Battery equalization interval – kept Disable
        5 Battery equalized time-out – kept Disable
        6 Floating Charge Voltage – 27.2V

        Can you please confirm above setting will ok or not.

        1. Hi Rohitha,

          The setting is good for use.

          If you want to make the cells balanced, lower the charge voltage to 28.0V, and current 100mA.
          You are reading the cell voltages, is the pack with Bluetooth?

          Andy

      2. Hello, Andy. I have pattery pack 51.2v * 100Ah (2P16S). In the manual i see charging current 57,6v. I didnt see floating voltage. Is the floating voltage 55,2v or 56,0v better? And battery have 43,2v turn off.

        1. Hi Greg,

          57.6V as charge voltage is good, if you do have to set the float voltage, it can be 51.2V ~ 53.6V.

          Protection of low end voltage 43.2V is good.

          Andy

      3. Best way to balance lithium battery packs is to do a low discharge rate balancing. Run some led lights for a while. Once cells are balanced. Charge
        If battery doesn’t charge in a balanced fashion switch brands. Poor on board BMS you will never have balanced batteries and problems will only get worse. Once cells get too out of balance they won’t charge. Assuming you are using a battery that doesn’t give you the option to charge cells individually

        1. Battery cell balance only happens when the voltage difference is over 20mV.
          Open charge balance, with minor current, charge to 3.50 per cell slowly.
          Higher voltage will lead to one battery cell hitting the cell voltage limit first.

          This is called the “Top Balance”, but it is not necessary for most of the battery packs now.
          The battery cells are balanced before assembling.

          But if you assemble the battery cells by yourself, of course, it is necessary.

          Andy

  5. Hai, i have 12v 50Ah battery, can i charge with 25Amp charger or should i just use 10Amp charger .

    1. Hi Faiez,

      In most conditions, 25A (0.5C) charging is fine.
      But still, it is better to check with your supplier about the max charge current.

      Andy

  6. Hi Andy. Thank you for sharing your experience. I have 8 (Epcom Power Line RLB100-48) 48V 100Ah server rack batteries, split into 2 racks of 4. They are going into a Sol-Ark 15K which has 2 Battery inputs.

    I got everything hooked up except for the Solar Panels – which will happen soon. I am grid tied.

    Of my 2 banks of batteries, 1 battery in each rack is discharging pretty rapidly, while the other 3 are charging.

    What could be causing this?

    Thanks in advance for your help.

    1. Hi Ed,

      That is quite an unexpected condition…

      How much SOC do you set to discharge from the grid but not from the battery?
      And how do you connect the batteries in parallel?

      Andy

      1. Thanks for the response. I have 4 batteries connected to a single + bus bar and a single – bus bar connected to the Battery 1 input on the Sola-Ark 15k. I replicate this exactly for the 2nd input on the Sol-Ark.

        I’m using the default settings for the SOC. I will see if there is an anomaly with those when I get a chance.

        Thanks again

        1. Hi Ed,

          Since you are using a busbar, the balance between the paralleled batteries should be good.

          It is really weird that the batteries are not in the same charge/discharge condition.

          Can you take a photo or screenshot when this condition appears?

          Andy

      2. Good day Andy – i am a newbie – just want to ask what could be wrong with my system if my SOC is 100% and i put a kettle on (when its on battery mode) no solar or grid – the SOC drops to under 10 % –
        can you help me – my battery is a Cyclone C5 5kv 16 cells

        1. Hi Quinton,

          It is possible the SOC is not right.

          How much power is your kettle? For high power discharge, the battery voltage can drop instantly.
          Like LiFePO4 battery, full SOC, it can drop from 3.50V to 3.30V per cell.
          But the SOC of course will not be under 10%…

          How do you set the battery in your inverter? You may contact your battery supplier to see what is the problem.

          Andy

  7. Good day to you Andy , I have lifepo4 battery 12v and its charger rating is SAKO LiFePO4 Battery Charger MODEL CHG-1405 INPUT AC100V-240V-2.0A MAX 47-63Hz
    OUTPUT:14.6V 5.0A

    The Charger got spoit and I could not get the type of charger that came with it .
    What other charger can you recommend for me to be able to charge the battery back to normal?

    1. Hello Francis,

      You may get a charger online, ensure the output voltage is within 14.0V-14.6V, and the current is under your battery’s max current.

      Andy

  8. Hello Andy – I have four 12 volt LifePO4e batteries connected in series for a 48 volt electric outboard motor that is required to operate on our electric only lake. I have a 48 volt LifePO4e charger that is ADJUSTABLE and can charge up to 15 amps.
    I have noticed that if I charge each 12 volt battery to the maximum cutoff voltage of 14.6 volts that the internal BMS of each battery will allow, the electric outboard over voltage circuitry will alarm and the motor will not run BUT if I adjust the 48 volt charger to charge EACH 12 volt to about 14.1 volts, the electric outboard motor will run.

    My question is: Can I leave the charger on all the time to keep the 12 volt batteries at 14.1 volts as I am not sure when I just want to take a ride in the boat BUT I have heard and read over the internet that I will SHORTEN the life of the batteries because there are only so many “cycles” – not sure how many – or 10 years that the batteries are warrantied for and if the charger is basically keeping the batteries at a “float” level of my adjusted 14.1 volts, it is “cycling” the batteries constantly and the “cycle count” of the the batteries will be “used up” a long time before 10 years?

    If I use the boat and then charge the batteries to 14.1 volts and then don’t use the boat for days, they discharge to about 13 volts. It then seems to take a few hours for that 15 amp charger to charge the four batteries to 14.1. I noticed today that my batteries were at 13.2 volts after being charged to 14.1 volts four days ago and it took only 15 minutes to charge them back to 14,1 volts. I can live with a 15 minute charge if we decide we want to ride the boat but I am not pleased with a few hours BUT if I have to do that to make the batteries last the warranty period MANY cycles or 10 years, I will do that.

    For these reasons, this is why I am reaching out to you for your expert opinion – Thank you Ron

    1. Hi Ron,

      Since your charger is 48V, does 14.1V mean 56.4V for 4 batteries in series?

      14.1V to charge a single 12.8V battery is OK.
      After the battery is charged to 14.1V, without the charge current, the battery voltage will drop slowly to 13.2V ~ 13.4V.
      If the charger is on, it may start to charge the battery again.
      That is the key point, if the recharge happens frequently, I don’t think it will be good to the battery or the internal BMS.
      But if it is not often, it can be acceptable.

      Floating charge voltage under 13.6V is recommended.

      Meanwhile, a few days without charge will not lead to much energy loss.
      I am not sure why your battery needs to be charged for a long time just after a few days?

      Andy

    1. Hi Rangervac Technology,

      I don’t quite understand.

      Do you mean to connect 3 units of 12V Lithium batteries in series?

      Andy

  9. Hi, Ihave a 24V alternator 55A , and I want to charge my Lifepo4 24v battery using a Victron Orion isolated converter DC/DC 24V, 17 A . Is this ok? thanks in advance for your ansver, best regards

    1. Hi Aljosa,

      What is your battery capacity?

      As I am not familiar with the alternator or the Victron converter, please make sure the charge voltage and charge current are within the safe range of the battery.

      Andy

  10. Hi Andy,

    I have a SMA system (Sunny Island 8 with Sunny Boy 5000-TL21) connected to a Volta 280 ah (51,2V) with BMS. The charge vol set to 56V. There is no grid connected only PV supply. When battery is fully charged (100%) the system switches off likely due to over voltage. What settings can be done to solve the problem ?

    1. Hello Ben,

      Do you mean the battery is off because of over-voltage protection?
      But even if the battery is shut down, it only shuts down the charge circuit, it can still be discharged to support your inverter.

      If the battery cells are not balanced, you may try to balance the cells by low current and lower charge voltage.

      Andy

  11. Hi Andy,
    Thanks very much for this your article. Its one of the very best I have read on cells and battery charge.
    I have one question please. I have a battery of 4 cells 12V 6Ah, i want to charge it with 12V, 100 Watts PV. at peak charge rate, the current can reach 6A. But from what I have read on this blog it seems it will be too high for the battery. I would like you to advice me on the maximum PV wattage at 12 volt that I can Use.

    Thanks to all those who commented as well I also gained from the solutions proffered to your questions

    1. Hi Robinson,

      Is your battery 12.8V6Ah?

      The charge current 6A can be fine, which is 1C, but please read your instruction from the manufacturer.
      The charge voltage should be over 14.0V to charge to full state.

      But for your 100W PV panel, the current can be over 7A, is it?

      Andy

  12. Hi Andy,

    I have 2 fairly new Lifepo4 10kw batteries and was initially advised by the reseller to use the 80-20% model and keep the batteries within this range.

    Recently I’ve been having issues with balancing between the batteries and was told to fully charge the batteries to 100% (which fixed the issue).

    The batteries have a BMS, and voltages are managed by the inverter.

    Should I charge up to 90% max and occasionally 100% for cell balancing?

    Thanks

    1. Hi Nash,

      By the issues with balancing, how much is the cell voltage difference?

      To balance the cells inside a fixed battery pack, the only way is to use the balance function in the BMS.
      It is recommended to charge the battery by voltage 56.0V (3.50V per cell) with very little current such as 100mA.

      But most people are not able to set the voltage or the current.
      The balance function will work slowly every time charged, maybe after a few weeks, the cells can be balanced.

      By the way, it is not necessary to keep the battery working at SOC 20% to 80%…
      10%-90% is the best range, and you can also charge it to full, no problem.
      If you can set the voltage, 56.0V (3.50V per cell) to full is wonderful.

      Andy

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