BU-802a: How does Rising Internal Resistance affect Performance?

Understanding the importance of low conductivity

Capacity alone is of limited use if the pack cannot deliver the stored energy effectively; a battery also needs low internal resistance. Measured in milliohms (mΩ), resistance is the gatekeeper of the battery; the lower the resistance, the less restriction the pack encounters. This is especially important in heavy loads such as power tools and electric powertrains. High resistance causes the battery to heat up and the voltage to drop under load, triggering an early shutdown. Figure 1 illustrates a battery with low internal resistance in the form of a free-flowing tap against a battery with elevated resistance in which the tap is restricted.



Low resistance, delivers high current on demand; battery stays cool.



High resistance, current is restricted, voltage drops on load; battery heats up.

Figure 1: Effects of internal battery resistance.

A battery with low internal resistance delivers high current on demand. High resistance causes the battery to heat up and the voltage to drop. The equipment cuts off, leaving energy behind.

Courtesy of Cadex

 

Lead acid has a very low internal resistance and the battery responds well to high current bursts that last for a few seconds. Due to inherent sluggishness, however, lead acid does not perform well on a sustained high current discharge; the battery soon gets tired and needs a rest to recover. Some sluggishness is apparent in all batteries at different degrees but it is especially pronounced with lead acid. This hints that power delivery is not based on internal resistance alone but also on the responsiveness of the chemistry, as well as temperature. In this respect, nickel- and lithium-based technologies are more responsive than lead acid.

Sulfation and grid corrosion are the main contributors to the rise of the internal resistance with lead acid. Temperature also affects the resistance; heat lowers it and cold raises it. Heating the battery will momentarily lower the internal resistance to provide extra runtime. This, however, does not restore the battery and will add momentary stress.

Crystalline formation, also known as “memory,” contributes to the internal resistance in nickel-based batteries. This can often be reversed with deep-cycling. The internal resistance of Li-ion also increases with use and aging but improvements have been made with electrolyte additives to keep the buildup of films on the electrodes under control. ( See BU-808b: What causes Li-ion to Die? ) With all batteries, SoC affects the internal resistance. Li-ion has higher resistance at full charge and at end of discharge with a big flat low resistance area in the middle.

Alkaline, carbon-zinc and most primary batteries have a relatively high internal resistance, and this limits their use to low-current applications such as flashlights, remote controls, portable entertainment devices and kitchen clocks. As these batteries deplete, the resistance increases further. This explains the relative short runtime when using ordinary alkaline cells in digital cameras.

Two methods are used to read the internal resistance of a battery: Direct current (DC) by measuring the voltage drop at a given current, and alternating current (AC), which takes reactance into account. When measuring a reactive device such as a battery, the resistance values vary greatly between the DC and AC test methods, but neither reading is right or wrong. The DC reading looks at pure resistance (R) and provides true results for a DC load such as a heating element. The AC reading includes reactive components and provides impedance (Z). Impedance provides realistic results on a digital load such as a mobile phone or an inductive motor. ( See BU-902: How to Measure Internal Resistance )

The internal resistance of a battery does not consist of the cells alone but also includes the interconnection, fuses, protection circuits and wiring. In most cases these peripherals more than double the internal resistance and can falsify rapid-test methods. Typical readings of a single cell pack for a mobile phone and a multi-cell battery for a power tool are shown below.


Internal Resistance of a Mobile Phone Battery

Cell, single, high capacity prismatic 50mΩ subject to increase with age
Connection, welded 1mΩ  
PTC, welded to cable, cell 25mΩ 18–30 mΩ according to spec
Protection circuit, PCB 50mΩ  
Total internal resistance ca. 130mΩ  



Internal Resistance of a Power Pack for Power Tools

Cells 2P4S at 2Ah/cell, 18mΩ subject to increase with age
Connection, welded, each 0.1mΩ  
Protection circuit, PCB 10mΩ  
Total internal resistance ca. 80mΩ  

Source: Siemens AG (2015, München)


Figures 2, 3 and 4 reflect the runtime of three batteries with similar Ah and capacities but different internal resistance when discharged at 1C, 2C and 3C. The graphs demonstrate the importance of maintaining low internal resistance, especially at higher discharge currents. The NiCd test battery comes in at 155mΩ, NiMH has 778mΩ and Li-ion has 320mΩ. These are typical resistive readings on aged but still functional batteries. (See  BU-208: Cycling Performance ) that demonstrates the relationship of capacity, internal resistance and self-discharge.)
 

GSM Discharge NiCd
Figure 2: GSM discharge pulses at 1, 2, and 3C with resulting talk-time
The capacity of the NiCd battery is 113%; the internal resistance is 155mΩ. 7.2V pack.

 

GSM Discharges NiMH
Figure 3: GSM discharge pulses at 1, 2, and 3C with resulting talk-time
The capacity of the NiMH battery is 94%, the internal resistance is 320mΩ. 7.2V pack

 

GSM Discharges Li-ion
Figure 4: GSM discharge pulses at 1, 2, and 3C with resulting talk-time
The capacity of the Li-ion battery is 107%; the internal resistance is 778mΩ. 3.6V pack

All three figures courtesy of Cadex

 

Notes:   The tests were done when early mobile phones were powered by NiCd, NiMH and Li-ion. Li-ion and NiMH have since improved. 

The maximum GSM draws is 2.5A, representing 3C from an 800mAh pack, or three times the rated current.

Last updated 2016-08-13

 

*** 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: BatteryU@cadex.com.  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.

Or Jump To A Different Article

Basics You Should Know
The Battery and You
Batteries as Power Source

Comments

On December 12, 2011 at 10:16am
Guillaume wrote:

If anyone could provide me with a link of a lead-acid battery internal resistance vs temperature, it would be awesome.

On December 13, 2011 at 6:37am
girish yadav wrote:

lead acid battery performs better at low intl resistance at low temperrature intl resistance rises while at higher temperature vice-versa.

On December 13, 2011 at 12:40pm
Guillaume wrote:

@girish

I should have been more explicite in my question. I already knew that a colder temperature meant a higher internal resistance (yeah, I know I should have mentionned it).

What I would like to know is by how much the internal resistance is affected by a change of temperature. For instance, take the internal resistance of a battery at 30°C (say 4mH).

What will it be at -40°C ? 2 times 4mH ? more than that ?

On November 28, 2012 at 11:48am
danwat1234 wrote:

Why is is that cheap aftermarket lithium ion polymer camcorder battery packs often, over time, get high internal resistance to the point where you can’t record that long in 1080p before the voltage lowers too much and the camcorder shuts down. If I wait a few minutes I can then do some more video.
Eventually though, internal resistance gets so bad that the battery just can’t deliver a large load for any amount of time.

This has happened to me with many aftermarket DB-L80 batteries. The charge cycles is something less than 100, probably around 75, and they aren’t exposed to high heat all that much except for summer.

What changes in a li-ion battery to cause it to wear out in the form of rising internal resistance instead of just reduced capacity?

On December 5, 2012 at 11:37pm
Tysen wrote:

danwat1234, the Batteries in question were most likely rated at a high Capacity but have very poor Discharge Rates. for instance the OEM batteries in a Li-ion drill are rated at only 1300-1500 mAH of storage, but are Capable of Delivering 10-15x their capacity (18amps) for a few mins. this is Just Like a starter Battery. Most Laptop batteries are rated around 2400-2600mAH and can Deliver usually 2x their total Capacity in amps which results in a 30 min Battery life when playing games (5200/0.5 =2600mah). now the aftermarket maker prob tried to sell you on a Larger cell. you did indeed get a larger cell but the Battery is unable too keep up with the demands of your camcorder.

On December 5, 2012 at 11:47pm
Tysen wrote:

Sorry to further Add onto this. Generally with the 18650 cells (most laptops use) the larger the Mah rating the lower the rate of Discharge. one of the things ive found from these cells is
1300 +/- 18 amps discharge rate
2000 +/- 10A
2200 +/- 6.5A
2400-2600 5A
2700+ 0.5-2A in a perfect world. and I have seen a Samsung 2900 mah cell with a 3A discharge rate. but it required a hobby charger to take it to the rated 4.35 volts and in standard systems it only ran 2640mah

On December 6, 2012 at 12:07am
danwat1234 wrote:

No they are regular sized DB-L80 polymer single cell batteries. They have just about the same capacity as OEM but internal resistance is higher. It’s just 1 of those things you have to look at when you buy $3 aftermarket 2.5 watt-hour batteries.
Thanks it’s interesting how higher density batteries can’t put out as much energy at once.

On April 14, 2014 at 3:28am
MUZAMMIL SALEEM wrote:

I want to deseal/open a lead acid battery without damaging. Is it possible? Is there any machine or specific tool available for this purpose.

On November 16, 2015 at 12:20am
Ankush wrote:

hey plz let me knw while discharging nicd cell why are we using resistive load and not inductive or capacitive?

On October 30, 2016 at 5:23pm
Tony Thomas wrote:

I am interested in sudden car battery deaths - over my 65 years, I have probably experienced six or seven.  Some appear to be a shorted cell, but maybe four or five were characterised by:

- suddenly won’t start the car at all
- often ageing, but working well the day before
- all lights go out when trying to start, BUT
- voltages test as NORMAL (except under load)

This has happened so often to me, and on the blogs it seems a NOT UNCOMMON type of failure

- YET I cannot see anything on good sites like battery university explaining this

I saw suggested that the joints between cells or plates can corrode - maybe this?
Does anybody have a technical analysis of this type of failure?