How does Internal Resistance affect Performance?

With the move from analog to digital, new demands are placed on the battery. Unlike analog portable devices that draw a steady current, the digital equipment loads the battery with short, heavy current spikes. 

One of the urgent requirements of a battery for digital applications is low internal resistance. Measured in milliohms, the internal resistance is the gatekeeper that, to a large extent, determines the runtime. The lower the resistance, the less restriction the battery encounters in delivering the needed power spikes. A high mW reading can trigger an early 'low battery' indication on a seemingly good battery because the available energy cannot be delivered in the required manner and remains in the battery

Figure 1 demonstrates the voltage signature and corresponding runtime of a battery with low, medium and high internal resistance when connected to a digital load. Similar to a soft ball that easily deforms when squeezed, the voltage of a battery with high internal resistance modulates the supply voltage and leaves dips, reflecting the load pulses. These pulses push the voltage towards the end-of-discharge line, resulting in a premature cut-off. As seen in the chart, the internal resistance governs much of the runtime.


  Figure 1: Discharge curve on a pulsed load with diverse internal resistance. This chart demonstrates the runtime of 3 batteries with same capacities but different internal resistance levels.

Talk-time as a function of internal resistance 

As part of ongoing research to measure the runtime of batteries with various internal resistance levels, Cadex Electronics examined several cell phone batteries that had been in service for a while. All batteries were similar in size and generated good capacity readings when checked with a battery analyzer under a steady discharge load. The nickel-cadmium pack produced a capacity of 113%, nickel-metal-hydride checked in at 107% and the lithium-ion provided 94%. The internal resistance varied widely and measured a low 155 mOhm for nickel-cadmium, a high 778 mOhm for nickel-metal-hydride and a moderate 320 mOhm for lithium-ion. These internal resistance readings are typical of aging batteries with these chemistries.

Let's now check how the test batteries perform on a cell phone. The maximum pulse current of a GSM (Global System for Mobile Communications) cell phones is 2.5 amperes. This represents a large current from a relatively small battery of about 800 milliampere (mAh) hours. A current pulse of 2.4 amperes from an 800 mAh battery, for example, correspond to a C-rate of 3C. This is three times the current rating of the battery. Such high current pulses can only be delivered if the internal battery resistance is low.

Figures 2, 3 and 4 reveal the talk time of the three batteries under a simulated GSM current of 1C, 2C and 3C. One can see a direct relationship between the battery's internal resistance and the talk time. nickel-cadmium performed best under the circumstances and provided a talk time of 120 minutes at a 3C discharge (orange line). nickel-metal-hydride performed only at 1C (blue line) and failed at 3C. lithium-ion allowed a moderate 50 minutes talk time at 3C. 


Figure 2: Discharge and resulting talk-time of nickel-cadmium at 1C, 2C and 3C under the GSM load schedule. The battery tested has a capacity of 113%, the internal resistance is a low 155 mOhm.

Figure 3: Discharge and resulting talk-time of nickel-metal-hydride at 1C, 2C and 3C under the GSM load schedule. The battery tested has a capacity of 107%, the internal resistance is a high 778 mOhm.
Figure 4: Discharge and resulting talk-time of a lithium-ion battery at 1C, 2C and 3C under the GSM load schedule. The battery tested has a capacity of 94%, the internal resistance is 320 mOhm. 

Internal resistance as a function of state-of-charge

The internal resistance varies with the state-of-charge of the battery. The largest changes are noticeable on nickel-based batteries. In Figure 5, we observe the internal resistance of nickel-metal-hydride when empty, during charge, at full charge and after a 4-hour rest period.
The resistance levels are highest at low state-of-charge and immediately after charging. Contrary to popular belief, the best battery performance is not achieved immediately after a full charge but following a rest period of a few hours. During discharge, the internal battery resistance decreases, reaches the lowest point at half charge and starts creeping up again (dotted line). 
  Figure 5: Internal resistance in nickel-metal-hydride. Note the higher readings immediately after a full discharge and full charge. Resting a battery before use produces the best results. 
References: Shukla et al. 1998. Rodrigues et al. 1999.

The internal resistance of lithium-ion is fairly flat from empty to full charge. The battery decreases asymptotically from 270 mW at 0% to 250 mW at 70% state-of-charge. The largest changes occur between 0% and 30% SoC. 

The resistance of lead acid goes up with discharge. This change is caused by the decrease of the specific gravity, a depletion of the electrolyte as it becomes more watery. The resistance increase is almost linear with the decrease of the specific gravity. A rest of a few hours will partially restore the battery as the sulphate ions can replenish themselves. The resistance change between full charge and discharge is about 40%. Cold temperature increases the internal resistance on all batteries and adds about 50% between +30°C and -18°C to lead acid batteries. Figure 6 reveals the increase of the internal resistance of a gelled lead acid battery used for wheelchairs. 


Figure 6: Typical internal resistance readings of a lead acid wheelchair battery. The battery was discharged from full charge to 10.50V. The readings were taken at open circuit voltage (OCV).
Cadex battery laboratories.

*** Please Read Regarding Comments ***

Comments are intended for "commenting," an open discussion amongst site visitors. Battery University monitors the comments and understands the importance of expressing perspectives and opinions in a shared forum. However, all communication must be done with the use of appropriate language and the avoidance of spam and discrimination.

If you have a suggestion or would like to report an error, please use the "contact us" form or email us at:  We like to hear from you but we cannot answer all inquiries. We recommend posting your question in the comment sections for the Battery University Group (BUG) to share.


On December 3, 2010 at 4:16pm
Antonio Sarasua wrote:

Hello, where can I find the Rerences: Shukla et al. 1998. Rodrigues et al. 1999?
Tahnks a lot in advance

On January 28, 2011 at 4:07pm
M.Nouman Ansari wrote:

Wonderfull Web I never saw before ,with full information Thanks

On February 25, 2011 at 9:58am
Ingo Kitzmann wrote:

Can you please provide me with a state-of-charge curve for a typical lithium-ion manganese cell, maybe discharged at 0.2C, 1C and 2C, with the voltage both measured under these discharge conditions, and as open terminal voltage.
If there is such a curve available: Is the open terminal voltage a reliable measure for the state of charge?

On June 10, 2011 at 2:28pm
Antonio Sarasua wrote:

Hello, is anybody here? please i need to know the full reference of Shukla et al. 1998. Rodrigues et al. 1999. THANKS!

On October 9, 2011 at 12:36pm
Roberlanio Melo wrote:

Gentlemen, what was the method used to measure the internal resistance of cell phone batteries?

On November 6, 2012 at 5:50am
Claudius Mudefi wrote:

hi guys, mine is not a comment but honestly i want to know if there is any advantage of a battery having a higher value of internal resistance.

On December 17, 2012 at 1:37am
gaurav wrote:

how internal impedence calculation is better than self dicharge voltage ?

On February 25, 2014 at 6:03am
Thegraj Govindasamy wrote:

Hi All

Please assist with the following related to flooded lead acid batteries;

1) Can an internal resistance test detemine state of charge of the battery.
2) Is it still necessary to do a Specific Gravity reading if the above confirms this?
3) What’s the relation between internal resistance tests and specific gravity tests.


On March 23, 2014 at 10:48pm
Rob David wrote:

I am flying my 450 helicopter with a set of 6 2.2A 3 cell 11.1V 30C Lipo Battery Packs which I monitor as carefully as possible. Post every flight I measure output voltage, IR of each cell, internal temperature and then I measure these same parameters pre and post charge.

This possibly seems a bit of an overkill but I am able to carefully see if any trends are occurring in any of my battery packs and I believe I have saved my helicopter exactly for this reason as one of my pack failed as I was spooling up the motor - as expected according to my recorded parameters.

I was expecting this failure because the one pack’s IR different between the 3 cells was getting progressively further apart and progressively more.  IR for the 3 new cells started of at 4,4,1 failed at 18,15,12. Knowing perilously little about battery electronics, I saw this as a sign of pending failure and I was, possibly by coincidence, correct.

But here is the real question.
If this parameter is as important as I think it is, How much difference between the 3 cells is too much? I am currently getting concerned when the max and minimum cell are 50% of each other. Is this too much or too little or am I barking up the totally incorrect tree here?

On August 20, 2014 at 9:36pm
YeonWoo Kim wrote:


I’m interested in Battery.
I have currious that how to look for State of Charge(SOC).
Could you please let me know a mathematical formula of SOC.

Thank you.

On November 23, 2014 at 12:06pm
dave backer wrote:

well, i think that there are many other things who affect performance, and they should be taken under consideration, green card lottery .

On July 8, 2015 at 2:31am
Sanjay wrote:

How to calculate IR of 12 volt ok battery
Example :- 12 Volt 130 AH SMF Battery

On July 24, 2015 at 1:11am
Angus wrote:

Please tell me how many number of internal resistance is standard of a new battery?
For example: 12V 60Ah car battery.

On September 30, 2015 at 8:25am
Aminos wrote:

Hi every one,
how can I estimate the internal resistance from some measured results such as voltage, current temperature… there any relationship between those parameters.

On October 13, 2015 at 9:01pm
Jake Willis wrote:

Cheers for helping me for 2b m8.
eternally grateful, your m8 Jake

On October 13, 2015 at 9:05pm
Jake Willis wrote:

Yeh, id just like to say thanks again for the help. I’ve spent the whole class sitting on tinder trying to organise a slam pig for this evening. Peace out, Jakey

On December 30, 2015 at 2:57pm
Ted Brown wrote:

I am measuring the internal resistance of a marine deep cycle 12 v battery. I want to know when is the resistance too high. I know a new battery is measuring about 4.5 m ohoms

On June 2, 2016 at 6:58am
Archie Goldswain wrote:

I recover used 12volt car batteries and recharge them using dhc smart chargers, I find that seemingly good batteries measuring higher than 10.5v take charge up to 75% but doesn’t top out at 100% where after the temperature rises and the battery is permanently lost. Intarnal resistance measures “Hi” or “Low” indicating the values are out or range. Please advise.

On December 2, 2016 at 10:15pm
Abhijeet Saxena wrote:

This article doesn’t include the internal resistance of the Lithium Ion cells with age, i.e., with number of discharge cycles. I think that is also a big factor in comparing the different types of batteries. It would be better if that is also included.

On January 5, 2017 at 6:23am


On February 8, 2017 at 12:51pm
DaBigDude wrote:

What is considered high IR and what is considered low IR.  I have a rack full of AA.  Some have IR of 40, some have IR of 600+.  At what point are the batteries effectively done and to be tossed/recycled?  They all still charge.  Some last longer than others in use.

On May 15, 2017 at 4:37am
Catalin Vladareanu wrote:

Hello to every one,

The internal resistance can be an indicator of the state of health of the battery (SOH) ?
What are relation between those.

Many thanks.

On July 2, 2017 at 11:06pm
Mayank Vyas wrote:

Hello Sir,

1.How to determine the diffusion rate and its after effects using EIS?
2. Is it possible to use EIS to determine the fault diagnosis of a battery ONLINE?

On January 14, 2018 at 2:10pm
Walter Saucier wrote:

Which AA will make my LCD flashlight shine brighter - eneloop Pro, standard eneloop 2000 mAh, or other NIMH AA? Does one have lower internal resistance than the others?

On April 20, 2018 at 4:53am
phil w wrote:

There’s an equation for calculating battery condition “Peukert’s” equation - based on his law. To properly measure charge in and out you would need an arduino running such an equation so time and current could be integrated. To do this you need a low ohm precision shunt resistor for measuring the current.

Internal resistance is only really of general interest when considering max current draw. I ran into a banana-skin using electronic flash kit. I tried NiMH. These are semi useless despite their claimed capacity giving very long re-cycling times. After research I resorted to NiCd which, for the Sanyo/Panasonic Cadnica AA, a minimal value for a new battery is claimed to be 15mOhms at 50% discharge. These really can deliver monster current and thus make the flash re-cycling times 1 or 2 seconds as opposed to the 10s of NiMh. Watch-it though, if the circuit was designed in view of NiMH and high IR then putting NiCd may overload the tansistors controlling the current so killing the device. Yes folks, Nicads are nasty polluting technology so I shall be careful as to how I dispose of then when their days are over.

On April 20, 2018 at 5:33am
phil w wrote:

Walter S - If the flashlight has any kind of regulating circuit - a buck-regulator for instance the brightness is set by the regulator’s current setting. An any battery chosen would not affect the brightness. If it has no regulator then Alkaline batteries would give a brighter output. This is due to their having around 1.5V open circuit whereas NiMh has 1.2V per cell.

On June 27, 2018 at 9:36am
Mr. Lam wrote:

I have measured the internal resistance using a internal resistance meter and I found when a battery is new the internal resistance is always zero. After sometimes of usage it will go up to more than 1 ohm. When it is more than 1 ohm it is time to replace the battery.
It apply to all kind of battery. Usually I due with 12vdc lead acid battery and Lithium battery.
Is it true?

The internal resistance must not more than 1 ohm using a internal resistance meter to measure. Is it true?

On July 1, 2018 at 12:27pm
phil w wrote:

Mr L: no battery has an internal resistance of zero. A bit of copper wire doesn’t have zero resistance. Even superconductors don’t have zero resistance - the have tiny resistance.