When you receive your new LiFePO4 (Lithium iron phosphate) battery, you might wonder about the battery’s voltage and state of charge (SOC). This article will show you the LiFePO4 voltage and SOC chart.
Let’s get started!
Manufacturers are required to ship the batteries at 30% state of charge. This is to limit the stored energy during transportation. It is also a good state of charge for the battery to sit at. This is because a lithium battery has a low self-discharge rate (less than 3% per month).
So when you receive a battery, it will be around 13 volts.
Now, you need the charge and discharge information of the battery. That’s why you are here. Your charger or charge controller requires more information to charge and discharge the battery properly.
Before giving you a voltage chart, you need to know that the discharge rate affects the voltage. If we discharge a battery at 1C, the voltage will be lower than at 0.2C. That’s why you should measure the voltage in an open circuit or with no loads attached.
This is the complete voltage chart for LiFePO4 batteries, from the individual cell to 12V, 24V, and 48V.
Download the LiFePO4 voltage chart here (right-click -> save image as).
Where to measure the SOC of the battery?
Always measure the state of charge at the battery terminals. This is because the voltage drop to other components like a charge controller or inverter can be high with such minimal fluctuations in voltage.
If the terminals of the inverter measure 13V but your battery terminals measure 13.2V, that’s a difference of 60% capacity!
What are the bulk, float, and equalize voltages of LiFePO4?
Some charge controllers do not have a dedicated Lithium setting. Therefore you can adjust the lead-acid parameters to match the lithium characteristics. It’s important to know that lithium only has bulk charging. It charges as much as possible, and when the battery is full, it stops.
The Bulk charge will be set at 100% SOC. The battery will be charged until this voltage is reached.
The float function for lead-acid batteries is there to keep the batteries topped up at a certain voltage because lithium has a very low self-discharge rate we can set it at 50% capacity. Because that’s the point where lithium is happy. You can also set it at 80-90% SOC. If you can disable it, do that.
The equalize function is also something for lead acid. If you can disable it, do that, but if you cannot, use the recommended voltages in the table below.
| 1 Cell | 12V | 24V | 48V | |
| Bulk/Absorb | 3.55-3.65 | 14.2-14.6 | 28.4-29.2 | 56.8-58.4 |
| Float | 3.375 | 13.5 | 27.0 | 54.0 |
| Equalize | 3.65 | 14.6 | 29.2 | 58.4 |
Bulk/absorb voltage is a range. Choose a lower range for a longer battery lifespan. Choose a higher range for more capacity.
Absorption time is not applicable for LiFePO4. If you have to set an absorption time, set it to 2 hours (source).
I guarantee this guide will save you $100s on buying the right components by having a good design and sizing.
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Increase the lifespan of your LifePO4 battery
Cycle life
Lithium batteries are known for their long cycle life of up to 6,000 cycles. After those 6,000 cycles, there will still be 80% of the capacity left. To put that into perspective, that’s 16 years of daily cycling of the battery.
Now, those 6,000 cycles are reached when you don’t discharge below 10% and charge over 90%. That means a 100Ah battery has a usable capacity of 80Ah to reach 6,000 cycles. If you use the whole capacity of the battery, then you can get 4,000 cycles, which still is a lot.
Temperature
You need to keep the temperature of the battery cool too. Going over 40°C or 104°F will make your battery age faster, thus decreasing its cycle life.
C-rate
The same goes for the charging and discharging rate of the battery. As you might already know, the C-rate is used for a battery’s discharge and charging speed. A 100Ah at 1C discharge is getting a load of 100Amps. The battery can handle this, but it’s not ideal.
Try to have a charging and discharging rate of 0.2C for your battery. This is a 20amp charge or discharge current for a 100Ah battery. One way to increase your charging and discharging rate is to increase your battery’s Ah (capacity). Buy a 280Ah cell, and you can charge and discharge at 56Amps for maximum cycle life.
To increase the capacity (Ah) of the battery put the batteries in parallel. To increase the voltage, wire the batteries in series. Read more about wiring batteries in series or parallel.
Compression
You might have heard about compressing the cells for increased lifespan if you build your batteries yourself. This is done at 300kgf (kilogram-force) or 3000 newtons. This doesn’t necessarily mean that you need to compress them. Using nylon tape around the cells is a great option. The idea here is to make it almost impossible for the cells to expand to limit gas formation.
LiFePO4 Charge Curve
Below you can see the charge curve of a LiFePO4 battery cell.
We can see that the voltage of the cell is very flat. That’s why it’s recommended to use a shunt in order to determine the battery state of charge (SOC). From the beginning of 10% to the end at 90% we will see a flat line. Before and after this point the voltage increases fast.
Sources:
I guarantee this guide will save you $100s on buying the right components by having a good design and sizing.
You can get the book for a reasonable price on amazon
I’m an off-grid enthusiast. I created this website to give clear and straight-to-the-point advice about solar power. I’m also the author of the book ‘Off-grid solar power simplified‘. Read more about me on my about page, check out my Youtube channel, or send me a message.
I got a 100ah LiFePo4, put a LiFePo4 charger putting out 1.5 amps, meter shows 13.6 max while charging, but when it said FULL I disconnected charger clamp and volt meter display showed 12.8VDC but jumped all over the place, up to 13.2VDC so is this brand new battery screwy?
It will take a long time to charge a battery with a 1.5A charger. Are you sure you put the right parameters in the charger? Did the charger stop charging when it reached 13.6V?
What is the c rating for 900ah lifepo4 batteries 3 300ah batteries in parallel
Hello Mike,
Parallel = Capacity gets added up.
So, 0.5C with a 900Ah battery will be 450A.
I have a KS Energy 205 AHr 12V LiFePO4 battery. It has bluetooth monitoring and according to the app it is at 90% SOC but the voltage is only 11.87V with no load. The individual cells are 2968, 2970, 2970 and 2970 mV. Temperature 8 deg C. Any idea why the voltage is so low?
Your battery looks to be empty. Is it possible to charge it without the BMS shutting it down at 100%. If that’s not possible you need to look into recalibrating the SOC. Normally, this can be done through the app of the BMS. It could also be in storage mode, refer to the manual how to take it out of storage mode.
If you have small loads the BMS SOC cant be calculated (the BMS dont have a real shunt, it only use a hall sensor) , you need a real shunt for that. ex. Victron Smart Shunt.
Hey Nick,
do you know which temperature is the lowest but not unhealthy for LiFePo4 loading? Ive heard about 5°C, are -1°C also possible and save?
thanks for answer 🙂
On the datasheet from EVE cells, we can see: Charging 0°C ~ 55°C, Discharging -20°C ~ 55°C.
Capacity and max cycle count are typically granted for “room temperature”, or, +25°C. I try to keep my batteries above 10°C by drivinǵ the solar charge to warming elements until the batt reaches +10°C. Cooling starts at +40°C and release at +35°C.
Hey Nick
in your article above there is a fault number in the tabe above the line “Increase the lifespan of your LifePO4 battery Cycle life”
in line 3 float the correct number at 48 V column should be 52,0 (V) , not 42.0V.
You are right Bert. Thanks for spotting!
Hello Nick –
Please I have a 48v Magnum Inverter with output power of 4300VA. I just replaced my flooded batteries with LiFePO4 (48V , 300ah, Rated voltage 51.6v, charging current 50A). Please what will be the setpoints of my bulk, absorb and float voltage? what will also be my re-bulk voltage. Please assist if you can.
Check out the end of the article where I write down these values for your 48V battery.
Hi Nick, great article and I use your Voltage Chart all the time.
Regarding the above question, I have two 48v LifePo4 Battery 155AH.
I couldn’t see your suggested Bulk (Absorption) and Float settings other than the Equalising Voltages.
One problem I have with one Battery is that it charges to around 85% SOC and one Cell goes rogue to 3650mv, the Battery OV’s and SOC jumps to 100%.
Have you ever come across this before? with any solution?
It’s in there just above ‘Increase the lifespan of your LifePO4 battery’
I haven’t experienced this. You have individual cells right? Have you top or bottom balanced them?
Hi Nick. Is it necessary to both, top and bottom balance the batteries?
I’ve got 4 batteries connected in parallel. they often reach 100% charge, but generally never drop below 40%
Also, is there any significant benefit to charging the batteries at 0.3c, as opposed to 0.4c? they are rated at 1c
You don’t need to balance if there is no significant difference between the cells at 0 and 100%. If there is a significant difference, then do a top balance. If you don’t have a BMS, do a bottom balance. I have written articles about balancing here.
You dont need to balance if there is no significant difference in the cells at 0 and 100%. If you have a BMS and there is a significant difference, then do a top balance. If you don’t have a BMS do a bottom balance. More info on balancing here: Bottom Balancing LiFePO4 There is no significant difference between 0.4 and 0.3C. Don’t worry about that.
Great notes and soc chart Nick!
I just upgraded from an old 24v lead acid battery setup to a new 24v lithium one (one of the 12v batteries in the bank gave up!).
Didn’t know what settings to use on my solar charge controller, or what cut off voltage to use for my grid tied inverter, until I found your article.
It’s very different settings compared to lead acid, so thank you very much for taking your time to share this and for being so thorough as it has helped me decide on the settings that suit my setup!
Thanks for the kind words Ford.
Great website! Great book! Great detail! And…Nick is always available to answer questions. He responds to emails daily, you won’t wait long for personalized guidance. Thanks Nick.
Thanks Richard. I appreciate the comment.
Hello Nick –
My 48v lithium battery mostly does not go below 51v DoD due to constant utility power supply which does not allow it to go lower than above while in use. Please will this in any way affect my battery lifespan as it mostly don’t get discharged before another charge up.
Thanks for responding!
Hello Steve, It will increase the lifespan of your battery. Going to 51V will be around 20% which is great. As you can read in my article here. I also recommend charging up to 90% (not 100%). You can do this by adjusting the charging parameters in your charge controller to 53.6V.
Thank you so much Nick – I guess the 53.6v mentioned above should be the float setting right?
Float is only applicable to lead-acid batteries because they have a high self-discharge. If you can, you should disable it on lifepo4. If you cannot, then use 54V.
Hi nick I have a 120ah lifepo4 battery charging off a 200w solar blanket. The battery is reading 13.1v and in great sunlight the best charge I can get is approx 2.5a to the battery. I would expect 8 to 10 amps from the blanket. Is there something I am missing?
Cheers
Adam
Is the voltage 13.1V without loads and no charge applied?
What kind of charge controller do you have? Is it embedded in the solar blanket?
I have four 3.2v 100 AH Lifepo4 batteries. They’re 6 years old. One has swollen up after I mistakenly left all four on a 12v trickle charger. I assume the swollen one is no good; the others charge to 3.34 or 3.35. Can I buy a new battery and connect it in series with the three that are good?
The one that is overcharged will have a reduced capacity. Placing the overcharged battery in series to make a 12V battery will be bad because the whole pack will suffer from it. You would constantly need to balance the cells. Depending on the severity of the case, this would be an external active balancer. Weird that only one swole, I assume because it had a lower capacity to begin with (no matched cells). If you left all 4 on a trickle charger in series, then there shouldn’t be a case of overcharging right? If you charged them in parallel, meaning 13.6V per cel ,then that is a problem. The cells would be severely damaged and capacity is certainly lost.
thank you very much, but I’m a little unclear about your answer. Are you saying it would be best to buy a new 3.2v 100 ah lifepo4 battery and that I can use it with the older batteries in a 4s or 12s configuration?
Hi Nick thanks for this information. I have a 2 batteries of 5kw each and the label show operation voltage range 44.8v to 57.6v, considering it what value you recommend for bulk and floating voltage ?
Check the table in the middle of the article:
bulk: 56.8-58.4
float: 54.0