# Battery impedance measurement

#### Prajeet Anand

Joined Aug 26, 2014
21
For the past few days I have been trying to buy a proper battery impedance measurement device that is good and also falls under my budget of 1000 dollars. I will be mostly using it to test 3.7V Lithium ion batteries. Could anyone suggest a good measurement device for that

#### Papabravo

Joined Feb 24, 2006
18,086
For the past few days I have been trying to buy a proper battery impedance measurement device that is good and also falls under my budget of 1000 dollars. I will be mostly using it to test 3.7V Lithium ion batteries. Could anyone suggest a good measurement device for that
I'm not sure what you are looking for and what the purpose is. If you are talking about the internal resistance then you can infer the value but AFAIK you can't measure it directly. Also, I don't think it is constant; an increase in internal resistance can be an indicator of End of Life. I suggest you familiarize yourself with the following:

https://batteryuniversity.com/learn/article/how_to_measure_internal_resistance

As you implied, there are instruments in the +$1000 category that will apply an AC signal and measure the AC current to infer impedance. A superficial look does not reveal any obvious sub$1000.00 candidates.

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#### crutschow

Joined Mar 14, 2008
29,484
Unless you measurement is critical, I would just use the DC load method.
Measure the open circuit voltage, and then the voltage and current with some resistive load.
The internal resistance is then simply the voltage difference divided by the load current.
This could be automated with a microprocessor or PC if needed.

#### Papabravo

Joined Feb 24, 2006
18,086
Unless you measurement is critical, I would just use the DC load method.
Measure the open circuit voltage, and then the voltage and current with some resistive load.
The internal resistance is then simply the voltage difference divided by the load current.
This could be automated with a microprocessor or PC if needed.
That's what I thought initially until I realized the TS said "impedance" which until today I didn't even realize was a thing. That and the existence of $1000+ instruments makes me question my initial reaction. #### BobaMosfet Joined Jul 1, 2009 1,944 That's what I thought initially until I realized the TS said "impedance" which until today I didn't even realize was a thing. That and the existence of$1000+ instruments makes me question my initial reaction.
Don't let the word 'impedance' fool you. All it means is resistance to the flow of current based on field effect, not thermal- which puts it in the AC domain.

#### Delta Prime

Joined Nov 15, 2019
1,326
Hello there
ac internal resistance (ACIR) measurements are quite common and somewhat standardized when measuring lithium-ion cells equipment needed is well over \$1,000 and very bulky and heavy.
dc internal resistance measurement lacks standardization and thus tends to be somewhat enigmatic,and generally misunderstood.
The cell’s ohmic resistance comes from the current collectors, the active materials of the electrodes, the ionic conductivity of the electrolyte, and other connections (like tab welds, contact resistances, and safety elements).
Electrochemical reactions and other phenomenon aren’t part of the ohmic resistance. These will each happen at different rates, and therefore aren’t dc, and will instead contribute to the ac impedance of the cell.
best practice test setup would be real world and practical,@crutschow suggestions would be the way to go for me.

#### crutschow

Joined Mar 14, 2008
29,484
All it means is resistance to the flow of current based on field effect
What "field-effect".

#### MisterBill2

Joined Jan 23, 2018
11,581
What you are actually wanting to measure is the battery internal resistance, or effective internal resistance. The method described in post #3 is all that you need. If you need to check a lot of batteries then an automated version of the same thing will be a better choice.

#### Papabravo

Joined Feb 24, 2006
18,086
Don't let the word 'impedance' fool you. All it means is resistance to the flow of current based on field effect, not thermal- which puts it in the AC domain.
It's not me it is Battery University that talks about it. Widely regarded as an authoritative source.

#### Papabravo

Joined Feb 24, 2006
18,086
What you are actually wanting to measure is the battery internal resistance, or effective internal resistance. The method described in post #3 is all that you need. If you need to check a lot of batteries then an automated version of the same thing will be a better choice.
That is what I thought initially, but measuring the AC impedance of a battery is actually a thing.

#### MisterBill2

Joined Jan 23, 2018
11,581
I wonder if that is a load drawing an AC current , or a pulsing load, or what? If the value has a number attached then the test conditions need to be specified. And that should help define the test.

#### Papabravo

Joined Feb 24, 2006
18,086

#### Audioguru again

Joined Oct 21, 2019
4,524
The resistance or impedance of a battery is in series with the load. So when a load runs slower or dimmer then the battery is worn out and needs to be charged more often or replaced.

A high quality Lithium Ion battery can do about 500 charge-discharge cycles and the internal impedance slowly rises so you might be dis-satisfied at 200 charge discharge cycles. People say that a cheap Li-ion battery operates poorly after only 20 charge-discharge cycles.

A Li-Ion battery fades away if it is stored fully charged for longer than a couple of months or if it has run down to a voltage below 3V per cell. I store my lithium rechargeable batteries at 3.7V to 3.8V over the winter when I do not use them.
I have some Li-ion batteries at 3.7V for 14 years and they still work well when I charge then discharge them.