BU-402: What Is C-rate?

Observe how the charge and discharge rates are scaled and why it matters.

Charge and discharge rates of a battery are governed by C-rates. The capacity of a battery is commonly rated at 1C, meaning that a fully charged battery rated at 1Ah should provide 1A for one hour. The same battery discharging at 0.5C should provide 500mA for two hours, and at 2C it delivers 2A for 30 minutes. Losses at fast discharges reduce the discharge time and these losses also affect charge times.

A C-rate of 1C is also known as a one-hour discharge; 0.5C or C/2 is a two-hour discharge and 0.2C or C/5 is a 5-hour discharge. Some high-performance batteries can be charged and discharged above 1C with moderate stress. Table 1 illustrates typical times at various C-rates.
 

Table 1: C-rate and service times when charging and discharging batteries.
 
C-rate Time
5C 12 min
2C 30 min
1C 1h
0.5C or C/2 2h
0.2C or C/5 5h
0.1C or C/10 10h
0.05C or C/20 20h

The battery capacity, or the amount of energy a battery can hold, can be measured with a battery analyzer. (See BU-909: Battery Test Equipment.) The analyzer discharges the battery at a calibrated current while measuring the time until the end-of-discharge voltage is reached. For lead acid, the end-of-discharge is typically 1.75V/cell, for NiCd/NiMH 1.0V/cell and for Li-ion 3.0V/cell. If a 1Ah battery provides 1A for one hour, an analyzer displaying the results in percentage of the nominal rating will show 100 percent. If the discharge lasts 30 minutes before reaching the end-of-discharge cut-off voltage, then the battery has a capacity of 50 percent. A new battery is sometimes overrated and can produce more than 100 percent capacity; others are underrated and never reach 100 percent, even after priming.


When discharging a battery with a battery analyzer capable of applying different C rates, a higher C rate will produce a lower capacity reading and vice versa. By discharging the 1Ah battery at the faster 2C-rate, or 2A, the battery should ideally deliver the full capacity in 30 minutes. The sum should be the same since the identical amount of energy is dispensed over a shorter time. In reality, internal losses turn some of the energy into heat and lower the resulting capacity to about 95 percent or less. Discharging the same battery at 0.5C, or 500mA over 2 hours, will likely increase the capacity to above 100 percent.

To obtain a reasonably good capacity reading, manufacturers commonly rate alkaline and lead acid batteries at a very low 0.05C, or a 20-hour discharge. Even at this slow discharge rate, lead acid seldom attains a 100 percent capacity as the batteries are overrated. Manufacturers provide capacity offsets to adjust for the discrepancies if discharged at a higher C rate than specified. (See also BU-503: How to Calculate Battery Runtime.) Figure 2 illustrates the discharge times of a lead acid battery at various loads expressed in C-rate.
 

Typical discharge curves of lead acid as a function of C-rate

Figure 2: Typical discharge curves of lead acid as a function of C-rate.
Smaller batteries are rated at a 1C discharge rate. Due to sluggish behavior, lead acid is rated at 0.2C (5h) and 0.05C (20h).
 

While lead- and nickel-based batteries can be discharged at a high rate, the protection circuit prevents the Li-ion Energy Cell from discharging above 1C. The Power Cell with nickel, manganese and/or phosphate active material can tolerate discharge rates of up to 10C and the current threshold is set higher accordingly.

Last updated 2016-07-25

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Comments

On April 29, 2011 at 9:22am
Luca wrote:

So the C-rates are just another way to express a current? 1C=1A (Ampere), 0.5C=0.5A= 500mA, 2C=2A=2,000mA ?

On August 22, 2011 at 11:49am
Matt wrote:

C-rates are the rate of discharge (or charge) as compared to the capacity of the battery.  A 1C discharge will be the current that would seemingly go through the rated ampere-hours of the battery in an hour.  A 2C rate is twice that current.  A 0.5C rate is half that current.  In the specific case of a 1 Ah battery given above, the numbers come out equivalent to amps, but in the general case, the C rate is different.  For example, a 5 Ah battery would (by rating alone) have a 1C current of 5 amps.  A 2C current would be 10 amps.  The 0.5C current would be 2.5 amps.  The real capacity of the battery changes with discharge rate though, so actual performance differes from the ideal capacity.

On September 14, 2011 at 11:02pm
amutha wrote:

how much charging time is required for 1 day back up of the rechargeable battery?

On October 21, 2011 at 8:31am
Crazy Casta wrote:

Your graph is confusing. Shouldn’t 1h=1C, 3h=0.333C and the 1C line be coincident to the 1h line?

On November 22, 2011 at 12:04pm
Srdjan Dragojlovic wrote:

I have system with 110pcs of 450Ah/2V in serial connection. I have problem with battery system. How I can find problematic battery?

On January 19, 2012 at 2:34pm
Howard Silverwater wrote:

With using a 38 Ah deep cycle lead acid battery and at discharge rate of 20 hours (ham radio 75% duty cycle; receive at 1.7A and transmit at 5.5A) with a solar panel supplying 0.8 A, why does a 12.25 V reading during transmit (5.5A) give a lower SoC (state of charge) than if I was NOT to consider the solar panel contribution and used HIGHER discharge rate (of ~14 hours)? According to typical lead acid graphs showing SoC vs. voltage while under discharge, a reading of the same 12.25 V shows a higher SoC for a faster discharge rate. I would expect an influx of 0.8 V from solar energy that contributes to slow down the discharge rate to show a higher SoC. What’s wrong with line of thought?

On February 12, 2012 at 6:00am
Johny wrote:

So, to achieve the desired C-rate, the batteries must be connected in parallel circuit…

If I ‘ve got 4 x 0.5C batteries with 12V, I can set a combination to 2C and 12V. Is it correct understanding?

On March 8, 2012 at 12:23pm
Jon wrote:

Johny—
I believe that in your example you’d still have a 1C battery (pack).  Assuming the following batteries:
  (4) 12V, 10AHr batteries (1C: thereby capable of delivering 10A over 1Hr)
Hooking them up in parallel, you’d end up with a configuration that is:
  (1) 12V, 40AHr battery pack (1C: thereby capable of delivering 40A over 1Hr).  Therefore, you’d still have 4x the current capability of a single battery (40A, instead of 10A), but it would not be possible to drain the pack in about 1/2 hour (as with a 2C battery), or about 15 minutes (as with a 4C).

On March 15, 2012 at 10:32am
gianni pup wrote:

On Li-ion battery cell technical specification I found the following charateristic :
Standard charge = ” Standard charge ” means charging the cell with charge current 1075 mA and costant voltage 4.2 V. at 25°C., 0.02 cutoff.
Could someone explain me the meaning of cutoff ?
Many thanks in advance !

On April 14, 2012 at 9:58pm
gurivireddy wrote:

Hi,
can some if explain me what happens to the C-rating if I connect two identical batteries in series, and in parallel.
do they change or they remain same?

thanks in advance

On May 4, 2012 at 3:06pm
styvens wrote:

@ Jon
your quick example is much more explanative than the whole paragraph who seems to circle around…

On May 16, 2012 at 2:19pm
Steve Spence wrote:

The term everyone seems to be dancing around is peukert. If you have a 100ah battery at the c20 rate, you can discharge at 5 amps, for 20 hours. If you pull faster, you’ll have less capacity, if you pull slower, you’ll have more. You can calculate this at http://green-trust.org/peukert/

On May 28, 2012 at 1:48pm
MySchizoBuddy wrote:

What about min and maximum charging current for a particular battery capacity.

On September 6, 2012 at 3:13am
hifasath wrote:

sir ,,
        i had on no of 12v 150ah c20 & 2 nos of 80 ah
which will make better performance

On March 26, 2013 at 12:01am
thinira wrote:

can anyone explane what is charge capacity, discharge capacity and coulombic efficiency?

On May 22, 2013 at 11:40pm
gunwoo wrote:

1C is a 1000mAh battery in one hour to supply 1000mA when you when 0.5C, 2C change when going to both the current time and why? When the total current 1000mA La 0.5C to 2C if ilttaen 2 hours 30 minutes 1000mA 1000mA supply is wondering whether or not haneunge?

On July 10, 2013 at 3:21pm
Olddawg wrote:

I came her to understand what a 1C is compared to a C1 rate.
What I understand is that it’s only an invert stat that means the same.

A C20 battery, which I work with, is a battery rated at a 20 hour draw.
Then could be stated as 20C

A 1C battery is the Ah at 1 hour draw
Then could be stated C1

It all comes down to the amount of time the battery can be drained.

Drain your battery, time it.
That’s your real C rate of use.
Want to improve the result because it’s under-performing??

De-sulfate the battery.

On July 15, 2013 at 8:33pm
Jason wrote:

On March 15, 2012 at 10:32am
gianni pup wrote:
On Li-ion battery cell technical specification I found the following charateristic :
Standard charge = ” Standard charge ” means charging the cell with charge current 1075 mA and costant voltage 4.2 V. at 25°C., 0.02 cutoff.
Could someone explain me the meaning of cutoff ?
Many thanks in advance !
===============================
In the case of your Lithium-ion charge, it interprets as the charger will begin from Constant Current(CC)mode, at the point when the voltage reaches 4.2V, the charger switches to CV(constant voltage) mode; the charge process won’t end until the current drops to the threshold of 0.02(20mA)

On November 18, 2013 at 12:27am
naresh wrote:

can any one explain, how do we choose the C rates, when we are developing the new battery. I Mean we do not know how much capacity it can store, in this case how we can choose the C rates.

On November 18, 2013 at 1:54pm
Olddawg wrote:

You don’t choose C-Rate. The response of dis-charge determines the C-Rate.

Since you’re developing a ‘new’ battery (of which I’d love to char further), I would start dis-charging small and work your way up.

You only know what you anticipate from the battery.
I used half that to draw and time it.
You may find you are correct and it draws 30-40+hrs before done.
Then you have a C30-C40 battery.

Up the draw till you hit the 20hr time length.
Now you have the draw matched to the battery.

‘Done’, becomes the next question..
I’ll await..

On November 18, 2013 at 11:45pm
naresh wrote:

Thank you for your replay mr. Olddawg.

You mean to say that we have to select the charging current such that it can full charge (100% capacity) the battery in 20 hr. Once we do this we will find out the full capacity of battery and according to this full capacity we have to select the C-rates. Initially I thought that we need to select the C-rates according to the theoretical capacity of anode and cathode (combined capacity) do we select C-rates according to theory?.

On November 19, 2013 at 2:22pm
Olddawg wrote:

You’re in new territory for me with a newly designed battery!
You’re thought of using the theoretic capacity is good for charging.
I still would go lighter and time it.
You may again find it will take 30hrs, yet better that going full and charging in 10hrs and slamming the battery with too much.

To me (MHO), the real test of capacity is going to come with dis-charge.

Without knowing what you truly have as a concept, and the possibilities being abundant, it’s difficult to say “Do this”...

Initial charge of something I just built, personally, I’d have a hard time going over 50% of what I believe it will do. Especially for the first run..
I’ve burned out too many good ideas (circuits) because I ms-judged the capability. 

I wish you great success in your endeavor!
Please keep me posted as to your results.

 

On November 19, 2013 at 10:15pm
naresh wrote:

Thank you,

Actually I am new to this field. That is why I am getting these silly questions and I am learning slowly and after that only I will start making the battery.

  One last question is that while calculating the theoretical capacity of a new battery do we take only cathode capacity or only anode capacity or combined capacity.

On November 20, 2013 at 3:32pm
Olddawg wrote:

Oh so many more questions…

What is the seperation?
What is the solution involved?
How is it being circulated?
Area of plate (if plates are involved)?
Quality of all?
Many more could come..

Oh my!
It’s not just as simple as capacity of either.. or both combined..

If no one else here ‘chimes in’ and you wish to continue..
Please send me a personsal email.
I will hook you up with some very good minds I work with!

Let’s see if this site can get you going first.
If not, write me!

 

 

 

On January 17, 2014 at 3:09am
Anne wrote:

I am also new on developing new batteries and have a similar question.

We have two devices: the old we used for CV and impedance and with the new (better) one we can also measure e.g. constant current measurement.

So when we want to start a test with the new device we have to add a c-rate. Since we do not know the capacity of the test cell, do we first have to measure CV on our old device to know the highest achievable capacity, so that we can calculate e.g. 0,1C?

And:
On our old device every cycle of one test cell needed the same time. In the first tests with the new one we noticed that the time for one cycle depends on the capacity of the cell (so a short cycle shows less capacity in the capacity-cycle-diagram). Does this mean that the new device notices when all active material has reacted and automatically starts the charging process, or what else can be the reason?

On January 20, 2014 at 6:04am
Jaan wrote:

The C-rating has nothing to do with the physical unit “coulomb”, so the first sentence of the article is misleading. 1 C is indeed the standard abbreviation for the SI unit 1 coulomb, but in this article, the notation 1C is used to mean a totally different thing! “Coulomb” is a unit of charge; it is just another word for ampere-second and could be used for measung battery capacity instead of milliampere-hours: 1 coulomb = 1 A * 1 s = 1 A * 1/3600 h = 1/3600 Ah = 0.278 mAh. What is denoted by 1C in this article, has actually the units of frequency, i. e. 1C (in this article) = 1/(1 h) = 1/3600 Hz = 0.278 mHz (millihertz).

On January 27, 2014 at 5:43pm
Steve wrote:

It sounds like to me you need to know the theoretical capacity of your battery before charging/discharging to apply this system? Is it possible to test your battery’s capacity using different C values if you are testing new anode/cathode technologies?

On January 28, 2014 at 1:22am
Anne wrote:

@Steve:
If you just run cyclic voltammetry (potentiostat) you do not need any capacity value, you get it from this experiment. If you use a battery cycler you need a C-rate (so: yes, using different C values is possible, most people does). If you need the theoretical capacity of your system (e.g. for Li-S, in the literature) or the capacity for your exact testcell I don’t know (that’s one of my questions).

On January 29, 2014 at 2:37pm
Steve wrote:

@Anne:
Thanks for the response!
I am at the same place you are then smile
When you run cyclically (potentiostat), I assume you then get the capacity related to the current over time?
Do you know how this compares to a “typical” charging profile where you hold the current (then the voltage) constant? http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

Bump for the question on a method to calculate the theoretical capacity!

On January 30, 2014 at 12:28am
Anne wrote:

(Do you use skype? If yes we can also discuss there. -  It would be awsome if a discussion of e.g. batteries could be done between different scientist via skype or something else, so that everyone get soon help…)

Hm, I just tell about our devices, maybe this helps you. If we run cyclic voltammetry in our old device we just have to add the parameters voltage range, scan number, Esteps and scanrate. Than you get a diagramm in which the voltage is the x-axis and current is the y-axis. Than you just have to calculate the area under the redox-peaks and with this (and the active mass) calculate the specific capacity.

If we use our new device we get a diagram in which the time is the x-axis, one y-axis is capacity and the other one is the voltage. Before the measurement here you have to add a c-rate. I guess it is like this: If you take the theoretical capacity of your system (Ah/g), transform this to your actual active mass you get the number you need for e.g. 0,1C.

Right now I can not tell you more, I do not really know what this fig.1 in the link is (but I work not Li-ion batteries).
Does this help somehow?

On February 27, 2014 at 4:02am
harry potter wrote:

do you use skype? If yes we can also discuss there. -  It would be awsome if a discussion of e.g. batteries could be done between different scientist via skype or something else, so that everyone get soon help…
i just want to ask something about that battery and explain me how to make it in russia\
benelmokadem
harry potter movies in order

On April 14, 2014 at 8:20pm
Jagat Modi wrote:

Can any body share the the probability of lead acid automotive battery being exploded dusting cracking of an engine ? And also the same battery being used for DG starting with permanent float cum boost charger connected ?
And what are the SOP for lead acid batteries used for such applications ?

On April 14, 2014 at 8:23pm
Jagat Modi wrote:

Can any body share the probability of lead acid automotive battery being exploded durting cracking of an engine ? And also the same battery being used for DG starting with permanent float cum boost charger connected ?
And what are the SOP for lead acid batteries used for such applications ?

On April 16, 2014 at 4:42pm
Steve wrote:

@Anne:

I have been busy working over the past few months, if you still check this site i would be happy to try and get a discussion going on. I am somewhat hesitant to put my skype name or email up on a permanent online post, but I think there could be a way to get in contact at least through an email.

Let me know if you are still using this with a post! I plan on checking this page for a week or two.

On April 16, 2014 at 4:51pm
Steve wrote:

@anne:

In follow up I have some questions about the voltammetry; I plan on using the technique myself XD but in my initial learning I didnt see how it could be applied to a theoretical capacity. Wont the measurement only tell you the potentials at which reactions inside the cell are occurring? i.e. lithium insertion/removal? I think that you would need some sort of time scale to know the amount of charge you are putting into the batter? Or perhaps you are cycling until you no longer see a reaction taking place?

On April 17, 2014 at 5:00am
Anne wrote:

@Steve
Hi, I also was (better said am) busy, but I want to still write here.

First of all: what device do you use (can you give me a name or so)? As I wrote we have two different ones, so it depends a bit if its more of a battery cycler or a potentiostat (at least in this way we name or two ones).
... It would be best if we could write mails, please write me on this adress (just a note is enough, that I have your address): vi-friends.v.af(at)web.de
Since is address I normally don’t use, its just for such cases (I will write you back from another, so don’t wonder; I do not want to write my real one here, because I already get enough spam mail ; )

On April 17, 2014 at 5:04am
Anne wrote:

@Steve
(Ignore the mistakes, I wrote too fast…)
When you send me a mail I will reply with some images, this makes discussion easier (and I can not add pictures here, so mail is the best).

On April 17, 2014 at 10:01am
Steve wrote:

@Anne

I have sent an email to that address, let me know through that address if you have received it :D

I can answer your questions from this forum through that address if it works!

On July 29, 2014 at 5:24am
Yogesh Yadav wrote:

Dear All

we have battery charger of 270 V, 10 Amp,  i want to know that what no of batteries i can charge on this of 12V 7.5 AH.

On September 1, 2014 at 2:17am
subbareddy wrote:

dear boss

ihave one doubt is how can i calculate the charging current ampere and discharge current ampere iwill give the one ex:225ah,1.2v/cell how much the current ampere

On September 19, 2014 at 9:00pm
RK PILLAI wrote:

What is the rate of charging current for lead acid batteries of different capacities?
Is there any universal charging rate? If the manufacturer has not mentioned any rate of charging, how can I fix the rate?
kindly give me a reply.

On February 9, 2015 at 2:16pm
Marko Stanojević wrote:

The first paragraph of this article contains the reference to the unit of charge - Coulomb (C) which, in addition to not having any strict relevance for what follows, only creates a possibility for confusion with the charge-rate designation bearing the same symbol.

Since the conventional way of describing the battery capacity is in terms of (MetricPrefix)AmpereHours, the logical and intuitive way of describing the charge-rate is the introduction of C, the current which ideally fully charges a completely discharged battery in one hour, and expressing the charge-rate in relation to this quantity.

On June 19, 2015 at 11:49am
Larry Becque wrote:

This article needs some rewriting as it is confusing and never really answers the question in the title: what is the C-rate.  After introducing the Coulomb and correctly defining it as 1 amp / second = 1C (Coulomb) the article wanders in other directions leaving the reader with the wrong impression that the Coulomb and C-rate are the same.  They are not. 
Wikipedia defines the C-rate much more directly and clearly as:
https://en.wikipedia.org/wiki/Battery_(electricity)#C_rate
The C-rate is a measure of the rate at which a battery is being discharged. It is defined as the discharge current divided by the theoretical current draw under which the battery would deliver its nominal rated capacity in one hour.[29] A 1C discharge rate would deliver the battery’s rated capacity in 1 hour. A 2C discharge rate means it will discharge twice as fast (30 minutes). A 1C discharge rate on a 1.6 Ah battery means a discharge current of 1.6 A. A 2C rate would mean a discharge current of 3.2 A.

On September 29, 2015 at 1:31pm
Bibek wrote:

I really like this website. Thank you for sharing . However i was wondering how depending upon the C-rate the capacity of a battery changes? Like with higher C-rate capacity will decrease and lower C-rate capacity will increase? I read that resistance increases with higher C-rate but can i have detail explanation on the chemistry part and in electrical part too? Thank you in advance

On September 30, 2015 at 6:18am
Marko Stanojevic wrote:

I suggest that this article is edited as to drop the first three paragraphs, as C-rate does not have direct connection with the unit of electric charge, Coulomb, that also bears the same designation, C, as they do not add to understanding of C rate. On the contrary, they only add to possible confusion, as is reflected in some comments.

The primary reason for the introduction of the C-rate is the need to address the current with which a battery is being charged (or discharged) in terms that bear more relevance to that particular battery than just stating the absolute current value.

Since the load (I will use this term for both cases of battery being either charged or discharged as in both cases higher currents present similar challenges) is relative to the capacity of a battery, the C-rate is used to describe the discharge or charge current in terms relative to it’s capacity, that is, to the current that would, under ideal conditions, discharge a fully charged (or completely charge a fully discharged) battery in one hour. Therefore C-rate is a good way to really get a grasp on the load placed upon a battery, regardless of whether it is during the charging or discharging process.

C therefore, in this context, represents a way to describe current, not capacity of a battery, although it is particularly related to its capacity.

It is useful to describe a regimen in which the battery is being used regardless of its capacity, so two batteries of different capacities but of the same type can be, current wise, described in mutually comparable terms.

Of course, different types of battery chemistry have different requirements, or rather interpretations. of what actual load in fact represent a current of the same C rating.

Therefore, you will only need to know a universal, C-rate based characteristics of a given battery type (chemistry) and will be able to convert this to actual current values depending on the battery’s capacity.

On September 30, 2015 at 11:55am
Larry Becque wrote:

I agree with Marko, the first three paragraphs need to go or be rewritten as follows:

In the late 1700s, Charles-Augustin de Coulomb ruled that a battery receiving a charge current of one ampere (1A) passes one coulomb (1C) of charge per second. On discharge, the process reverses. Often in engineering terms, the letter C is used as a symbol for one Coulomb of charge but this should not be confused with the C-rate which is different. 

C-rate is defined as the charge / discharge current divided by the nominally rated battery capacity.  For example, a 5,000 mA charge on a 2,500 mAh rated battery would be a 2C rate.  A 2,500 mA charge on the same battery would be a 1C rate and would theoretically fully charge the battery in 1 hour (assuming 100% charge efficiency). 

The capacity of rechargeable batteries is commonly measured in Amp hours at a 1C rate particularly for Li-ion chemistries.  However, in some cases capacity is measured at a much lower C-rate typical of their intended use as in the case of small alkaline consumer batteries and sluggish lead acid batteries. 

On October 6, 2015 at 11:05pm
Hardware Freak wrote:

If I Discharge a Li-ion Battery at 0.8C, what will be the time taken to disharge 90% of the Battery capacity

On October 22, 2015 at 7:16pm
Robert Dubé wrote:

@Hardware Freak
Simple arithmetic will give you the answer;
1 / 0.8 * 0.9 = 1.125h in decimal time which is 1h 7m 30s (0.125 * 60 / 100)

But that is all very theorical; is the battery really charge to full capacity (is your charger calibrate?), C is from what is written on battery or measured? If written on battery, what are spec from manufacturer to calculated Ah (charged to 4.4v and discharged to 2.6v or 4.2v to 3.0v? and at which rate is it discharged?) and so on…

On November 26, 2015 at 5:35am
anaz wrote:

in c10 ratting how much oncharing volt is disconet?/

On January 14, 2016 at 4:13am
lal bahadur singh wrote:

can you explain in depth, how to test a new cell in lab. to understand it’s anode’/ cathode capacity, after fabrication of cell with graphite powder and liCOo2 cathode, thru battey analyser.THEMETHODOLOGYAND SETTINGS OF VOLTS AND CURRENT VIS A VIS ELECTRODE SAMPLE WEIGHT.

On January 15, 2016 at 2:24am
Roy Emmerich wrote:

Correction:

“At 1C, a battery rated 1,000mAh charges at a current of 1,000mAh.”

should read:

“At 1C, a battery rated 1,000mAh charges at a current of 1,000mA.”

On January 23, 2016 at 5:58am
Ren wrote:

“A new battery is sometimes overrated and can produce more than 100 percent capacity; others are underrated and never reach 100 percent, even after priming.”
I thin you meant it other way around.

If battery is overrated then in reality you would never achieved the mentioned charge/discharge. Like many of the chinese batteries. Some are rated at 5000mAh but achieve only 100mAh. These are overrated batteries.

On May 6, 2016 at 12:17pm
Danny Gonzalez wrote:

Thanks for this site. I refer to it often.

I’d like to be sure about charge voltages and I’m confused by the C rate designations. Is C rate defined by the specific mah capacity of each cell in a pack, or is it defined by the aH rating of the pack as a whole?

I’ve just bought a 13.2v 38ah lithium phosphate battery and it appears to be charge rated at C5. It seems that it’s made up of 26650 cells.The MFG spec states that 20v is the recommended charge rate and calls that C5. What is the acceptable charge range for it (Im expecting to end up with a disharge rate of around 14 hours in my application, should that matter)?

On May 11, 2016 at 9:43pm
Larry Becque wrote:

@Danny Gonzalez The information you provided is very confused but I will try and provide answers. 
1. C rate usually applies to the individual cells but can also apply to a pack made up of cells arranged in series and parallel.  The difference is that if you are charging a pack with two sets of cells in parallel (doesn’t matter how many are in series) you must apply twice the amperage to achieve the same C rate for charging.  When the cells are arranged in series the charge current (amperage) remains the same but the voltage increases by a multiple of the number of cells.
2. Not sure why your battery is rated C5 for charging.  LFP normally charge at 1C.  Check with the manufacturer.  Perhaps what they mean is that you have 5 sets of cells in parallel in the pack so need to apply 5 times the current you would apply to a single cell at the 1C rate.
3. 13.2V for the pack divided by 3.3V nominal Voltage for a LFP cell means that you must have your cells arranged in sets of 4 cells in series.  Assuming from the above that you have 5 sets of cells in parallel this means you have a total of 20 cells.  38Ah divided by 20 cells equates to 1,900 mAh per cell which seems reasonable.  So 1C would be a charge of 1.8A.
4. 20V sounds like way too much voltage to charge this pack.  LFP cells normally charge to 3.65V per cell max.  With 4 cells in series times 3.65V this means 14.6V would be the max voltage to apply to the pack.
5. Li batteries are charged at constant current then constant voltage with the current reducing.  The mfg should give you both an amperage and voltage limit for charging the pack.

On May 11, 2016 at 9:47pm
Larry Becque wrote:

correction:
3. ..... 1C would be a charge of 1.9A.

On May 13, 2016 at 3:41am
Marko Stanojević wrote:

Accidentally removed myself from the comments recipients list, as I had commented on this article previously and have been receiving notifications. I am interested in the development of this article/discussion. This is only for re-enlisting purposes, as I haven’t been able to find another way.

Sorry for the inconvenience.

On May 13, 2016 at 3:43am
Marko Stanojević wrote:

I accidentally removed myself from the comments recipients list, as I had commented on this article previously and have been receiving notifications. I am still interested in the development of this article/discussion. This is only for re-enlisting purposes, as I haven’t been able to find another way.

Sorry for the inconvenience.

On June 6, 2016 at 4:39pm
Anja Rindstad wrote:

An AGM battery has a C100 capacity of 240 kWh. What does that mean?

On June 10, 2016 at 6:41am
Marko Stanojević wrote:

C100 is the regimen that charges/discharges a battery in 100 h. The rating you provided means that, when the said battery is charged/discharged at C100 rate, it will store/provide 240 kWh of energy. This is, of course, implying that during such discharge, the rated voltage will remain just that - (practically) the same. Since you did not provide data regarding the battery’s rated voltage, I’ll provide a calculation for a case of a 12 V battery. The common way for describing battery capacity is in Ah. 240 kWh is 240 kVAh, which, for a 12 V battery, gives the C100 capacity of 240/12=20 kAh, or 20,000 Ah. From this we derive that the battery’s C100 rate is 200 A.

In conclusion, the battery whose (incomplete) rating you provided would, if it were a 12 V battery, have a C100 capacity of 20 kAh and a C100 charge rate of 200 A.

Hope this helps.

On June 14, 2016 at 2:01pm
Evan Kurtz wrote:

Not a battery person…looking a some spec sheet I see charging rate but C ratign talk about discharge rates…Can one assume there are the same?  My gut feel is no but it may depend on battery chemistry etc.

Thanks

On July 22, 2016 at 12:51am
Lucho wrote:

How can man calculate the maximum current in a battery working till DoD = 50%?
12 V 200 Ah with DoD = 50% C-rate = 5: In 5 hours I get E = 2400 Wh with I_max = 40 A or
E = 1200 Wh with I_max = 20A?

On August 8, 2016 at 5:06am
pooja wrote:

If i have a model which allows 10C charge/discharge rate, and i require only 3C, So can i do the sizing with respect to 10C i mean to reduce number of batteries. Please explain

On August 15, 2016 at 8:37am
Sakir Husain wrote:

Please said me, when i will battery HRD TEST, IF 180AH Battery Capacity , how can i selecte A3 c Ahmpere, 180*3=540 its ok, and cut of voltage 7.5 is proper Setting for HRD Result

On November 23, 2016 at 5:52am
Mike Chapman wrote:

I have a need to charge 12 or more AA NiH batteries in series to make a battery pack to simplify the charging process. What are the issues including the charging rate and duration. Are there any safety issues?