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Evaluating Battery Test Equipment – Introduction

Batteries are a critical component of many products, and energy storage plays a very active role in our lives even outside of the research/industry setting. Therefore, selecting the right battery test equipment is an important decision for companies and the individual researchers who are responsible for producing results, whether they are starting small, or at massive scale.

The expert engineers at Arbin have been advancing the benchmark of “state-of-the-art” battery test equipment for over 27 years. We are defined by innovation, from being the first to apply multiple current ranges on a single test channel to more recently being the only company to offer true high-precision testing for high current applications, and supporting “Turbo Mode” with smart battery modules. We continue to learn from our industry partners and work with them on key technology breakthroughs.

The following report shares some of this knowledge using plain terminology and illustrations. Here are five key topics to consider when choosing battery test equipment:

Click to download the full report:  "How to Evaluate Battery Test Equipment."

1.  Hardware - Specifications & Quality of Materials [Continue Report Preview]

2.  Software - Usability and Features

3.  Data - Logging, Management, and Analysis

4.  Options - Auxiliary Features and Accessories

5.  Support - Product Safety and Support

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Evaluating Battery Test Equipment 6: Software

Easy to use drop-down lists to build test profiles

All battery test equipment requires software to operate the instrument.  The software interface can be one of the main differentiating points besides hardware performance.  It is important to confirm the software communicates using a modern high-speed standard such as TCP/IP (Ethernet) protocol and whether high-performance microcontrollers are used internally.  This helps future-proof the system as well as meet the bandwidth necessary for fast data logging.

A software user interface should use familiar commands and follow a logical process to create tests, but also needs the flexibility to control advanced test protocols.  The best software will not restrict the researcher to pre-defined test parameters, but will give full authority over the equipment’s voltage and current control.  The following questions will help identify a complete feature-set:

  • Simple method to implement drive cycle or other simulation

    Are capacity and energy calculations made at the micro-controller level or post-processed data?

  • Is there a limit on the number of steps per test?
  • How can an EV drive profile be performed?
  • Do tests utilize branching and looping conditions?
  • Can tests utilize multiple condition like this for each step and combine logical functions?
  • Can tests use mathematical functions?
  • Can the software use meta-variables instead of numeric values only, such as stopping a test based on

    Easily group any number of channels in parallel

    “80% discharge capacity” instead of only a numeric value?

  • How many of these meta-variables are offered?
  • Can tests be controlled using C-rate values instead of amperage if the cells under test vary in capacity?
  • Can channels be connected in parallel to increase the current capability? If yes, then how many?

Arbin allows all these methods and more to apply dynamic and complete control of voltage, current, power, & load, and offers user-defined variables in addition to the 90+ standard meta-variables.

(1) Resolution | (2) Precision | (3) Temperature | (4) Robustness | (5) Accuracy | (6) Software

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Evaluating Battery Test Equipment 5: Accuracy

Accuracy represents the trueness of test equipment measurement; the closeness of average sample to its true value.  Specifying this metric requires comparison to a known source such as a high-performance meter.

Plot of -200A discharge pulse on two different testers.

Plot of -200A discharge pulse on two different testers.

Accuracy should not be confused with noise. The relationship between “accuracy” and “precision” relates to the measurement noise. As stated above, accuracy is how close the average measurement is to the true value largely ignoring noise.  Precision specifies to the amount of noise that will be present.  Therefore, an instrument with good accuracy can still have a noisy measurement if it has poor precision and can be affected by temperature fluctuations.

Translating this into test results...
Note the plot and description above.  Many types of battery test equipment will have similar accuracy specifications, and while this is important, it should be evaluated in combination with the instrument’s resolution and precision.  The accuracy metric alone can hide the true performance difference of the equipment.

Calibration is another related factor to question during evaluation.  Battery test equipment that is sufficient to use a simple hand-held meter during calibration will not produce results any better than the meter.  Arbin calibration requires a 6.5 digit or better digital multi-meter and some equipment will require 8.5 digit or better.  NIST-traceability is maintained for meters used in all factory calibrations.

Inadequate meter for calibration

6.5 digit (or better) meter should be used for calibration.

(1) Resolution | (2) Precision | (3) Temperature | (4) Robustness | (5) Accuracy | (6) Software

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Evaluating Battery Test Equipment 4: Robustness

Robustness - the quality of materials and quality of construction have a major impact on how long the test equipment lasts and how long it will hold calibration.

Resistance to corrosion and temperature fluctuations are significant attributes of high-quality test equipment.  The instruments duty cycle and the maximum power rating also heavily contribute the usefulness and longevity of the equipment.
Long-term battery testing requires test equipment to run continuously.  Modern batteries are designed to run  for thousands of cycles at a minimum, while xEV and grid storage applications require batteries to last 10’s or even 100’s of thousands of cycles.  High-quality test equipment that can operate without interruption is necessary for such applications.  Likewise, the power demands for modern batteries make it important to verify the max power rating of test equipment.  Many will not be rated to operate at a maximum calculated power (max voltage x max current), especially with a 100% duty cycle.

Low quality equipment is known to have a high failure rate and may not hold calibration.  Frequent calibration checks and re-calibration will be required, which affects the validity of results data.  Replacing failed test equipment on a regular basis also affects the validity of test results across this period.

Arbin 96-channel cycler using bipolar circuitry and designed for continuous operation.

Arbin 96-channel cycler using bipolar circuitry and designed for continuous operation.

Translating this into test results...
Arbin testers have corrosion resistant coatings on all circuitry.  The high-quality materials offer better natural resistance to temperature fluctuations and some products have special thermal management technology inside for sensitive components (ask your Arbin sales rep for more information).  Arbin test equipment is also engineered to run continuously on a 100% duty cycle and is rated to operate at maximum power (full voltage, full current output).

The true bipolar circuitry used by Arbin eliminates the switching time between charge and discharge.  It also increases the longevity of equipment since relays are not switching during test profiles with frequent charge/discharge such as drive profile simulations.

(1) Resolution | (2) Precision | (3) Temperature | (4) Robustness | (5) Accuracy | (6) Software

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Evaluating Battery Test Equipment 3: Temperature

Temperature variance of the test equipment and the device under test will always affect the measurement.  This is a physical property that cannot be escaped, but it can be minimized.

Current -vs- Time plot

Knowing how temperature affects the measurement empowers the researcher when determining the experimental error. When test equipment resolution and precision are sufficient, measurement fluctuation due to temperature will be seen. Gradual temperature changes will gradually skew results data [above], and sudden temperature changes can cause jumps in the data as seen [below].  It is important to use test equipment that is resistant to temperature changes with proper thermal control mechanisms and to control temperature of the test environment.

Translating this into test results...
Arbin defines the affect of temperature on the instrument accuracy as ~0.000185% / 1°C, by using patented shunt designs and high-quality materials that are resistant to temperature fluctuations.  Additionally, some of Arbin’s test equipment uses internal thermal control mechanisms that isolate sensitive components and tightly regulate the temperature using techniques developed during a multi-year investigation with partners Ford Motor Company and Sandia National Lab’s metrology department; regarded as one of the best in the world.  This technology allows the test equipment to maintain incredibly high precision measurements.

Current -vs- Time plot

(1) Resolution | (2) Precision | (3) Temperature | (4) Robustness | (5) Accuracy | (6) Software

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Evaluating Battery Test Equipment 2: Precision

Precision determines the level of noise/fluctuation present in the test equipment’s measurement.  Precision also indicates the consistency and repeatability of the instrument’s measurement circuitry.  A measurement with very little noise/fluctuation is considered to be precise.  Measurement precision at “100ppm” indicates it will vary by no more than 0.01% (100/1,000,000).

Many instruments will not specify their precision, which is a warning sign, or will improperly report precision though multiple averaged calculations or very slow frequency data logging that hides the noise.  Another common tactic is to report precision of battery coulombic efficiency calculations instead of hardware specification. These practices are misleading and reflect negatively on the company’s reputation.  [Ask to learn more.]

The test equipment resolution, quality of materials, and thermal management all play a significant role to provide superior precision.  Precision should be specified directly for the voltage, current, time, and sometimes temperature measurement of the test equipment.

Translating this into test results...
Arbin defines the measurement precision for voltage, current, and time for each class of test equipment.  These are the three parameters measured by the test equipment that define its performance.  Quartz timing crystals are used for measurement and timestamp; representing the state-of-the art method for such measurements.

The benefits of high-precision measurements during battery research have been widely discussed in academia for almost a decade.  Coulombic efficiency and differential capacity are two metrics that have been shown to require incredibly high precision test equipment to be meaningful and draw confident conclusions. These analytical techniques can miss or obscure signatures in the data if experiments are conducted with low precision test equipment that will generate noisy and inconsistent (unrepeatable) results.

(1) Resolution | (2) Precision | (3) Temperature | (4) Robustness | (5) Accuracy | (6) Software

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Evaluating Battery Test Equipment 1: Resolution

Resolution indicates the smallest change in measurement that can be detected by the instrument’s sense and control circuitry.  Typically referred to in “bits” of resolution or an absolute unit of measurement such as µV or µA.

For battery test equipment, resolution is determined by the analog to digital and digital to analog conversion, commonly known as ADC and DAC, of the sense circuitry and control system.  Analog signals vary at a continuous (near infinite) rate while a digital signal varies by a discrete rate that is measured in bits.  When zooming in to look at current/voltage/time measurement data, the bits of resolution are the smallest changes that can be detected, and while capacity, energy, internal resistance, etc. are not direct measurements, they are all calculated from the same data.

Translating this into test results...
Arbin’s 24-bit resolution means its circuitry can sense 1 part in 16,777,216 (2^24).  This is a 256x improvement over 16-bit resolution (1 part in 65,526), which is the industry standard.   Greater resolution produces greater clarity with more significant digits.  Higher resolution test equipment, when combined with high precision measurements, has the sensitivity to detect changes in voltage & current (as well as capacity, energy, IR, etc.) that would otherwise be missed, such as detecting a small spike in resistance as a battery approaches end of life, or a slight dip in coulombic efficiency that indicates end of life.  Many academic papers have been published by scientists who look for trends and identifying test metrics that can reduce the test time required during battery material development.  An upgraded tool with better resolution and overall performance should expedite this process even more.

(1) Resolution | (2) Precision | (3) Temperature | (4) Robustness | (5) Accuracy | (6) Software

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