Wandering through the jungle of fast charging protocols: Why „powerful“ is not always „fast“.

Once upon a time there were two wires and the most difficult part of charging was not to confuse plus with minus. Charging batteries today has nothing to do with that – along with plus and minus, there is a continuous conversation between the device being charged and the charging device. And this conversation, on top of everything, takes place in different languages, the so-called protocols.

And even before we get to this conversation, the hardware must be fully compatible: we use different chargers, cables, adapters from one standard to another… And even if we match everything, it may turn out that the charger provides the necessary protocol, but does not provide the full range of voltage and current for the most efficient charging. There are electronics in the cables themselves, some even have their own firmware that can be updated.

The wandering through the jungle of protocols for fast charging begins.

Cables are not what they used to be.

Of course, most users don’t care about this. For them, there are „branded“ chargers and cables, and „counterfeits“. They are willing to pay many times more for original chargers, thereby compensating for their ignorance. If you are one of these people, this article is not for you.

In fact, there are almost no counterfeits on the market

Hardware usually has a description, and it is true. The fact that someone does not understand what is written in the description does not make the hardware a „counterfeit“. A large part of users do not read what is written about the devices at all – be it cables, chargers or adapters. Yes, some manufacturers use marketing tricks to sell their products, but this does not make them guilty, nor their products – counterfeit.

Never forget that when you point your finger at someone, three other fingers are pointing at you! If you think the same way, I recommend that you continue reading and I hope that this reading will be useful to you, as I plan to try to explain everything simply, so that even I can understand it!

Let’s start with the cable

Plus and minus are no longer enough. You need at least two more, and for Type-C four more wires – D+, D- and CC1, CC2 (and let’s not forget one more – a common ground for everyone).

• D+ (Data Plus) and D- (Data Minus): These are the data signal lines in the old, classic USB standard (USB 2.0).
• CC1 (Configuration Channel 1) and CC2 (Configuration Channel 2): These are the configuration channels that are specific and critical only for the USB Type-C connector.

A detailed explanation of each of them:

A) The D+ and D- (Data Lines) pair

These lines were created to transfer data (for example, from a flash drive to a computer). However, in the pre-USB-C era, engineers found a way to use them for fast charging.

• How they work to charge: When you connect your old phone to a charger, they „negotiate“ for power using the voltage on these two lines. For example, if the charger outputs 3.3V on D+ and 0.6V on D-, the phone “knows” that it is a QC3.0 charger and can request 9V or 12V.
• Protocols that use D+ / D-:
  • BC1.2 (CDP): The oldest charging standard.
  • APPLE: Apple uses specific resistors on D+ and D- to indicate whether the charger is 5W, 10W or 12W.
  • Qualcomm Quick Charge (QC) 2.0 and 3.0: Rely entirely on the voltage levels on D+ and D-.
  • Samsung AFC: Same as QC2.0.
  • Huawei FCP: Uses a digital signal on the date lines.
  • OPPO/OnePlus/Realme (old versions VOOC / DASH / WARP): Uses a proprietary protocol on D+ and D-, which requires an original cable.

B) The CC1 and CC2 pair (Configuration Channels) 

This is the innovation in USB Type-C. These pins are the reason why USB-C is so smart and can be plugged in from both sides (reversible).

• How they work:
  • Orientation detection: When you plug in a USB-C cable, the charger measures which of the two CC pins is connected. This way it understands which side is “up” and which is “down” so it knows where to supply power.
  • Role detection: They allow the device to know whether it is plugged into a charger (Host) or another device (Peripheral).
  • USB Power Delivery (PD): This is where all the magic happens. The PD protocol doesn’t use the old data lines (D+/D-). Instead, it sends a digital code on the active CC pin (the other one is left for powering „active“ cables). Through this code, the charger and the phone talk to negotiate high voltage and high current (e.g. 20V @ 5A for laptops).
• Protocols that use CC lines:
  • USB Power Delivery (PD) 2.0 / 3.0 / 3.1: Fully digital signals on the CC line.
  • PPS (Programmable Power Supply): As part of PD.
  • Qualcomm Quick Charge 4.0 / 5.0: Since these standards are compatible with PD, they also use the CC line.
  • Chinese fast protocols (Huawei SuperCharge, OPPO VOOC) in modern USB-C versions: Some of them also use CC to recognize the original cable or for compatibility with PD.

The difference between BC1.2 DCP and CDP 

The BC1.2 (Battery Charging 1.2) protocol can be either DCP or CDP. Here’s what it means. There is a significant difference between DCP and CDP, but the commonality is that both allow charging with a higher current than the standard USB 2.0 (which is only 500mA).

DCP (Dedicated Charging Port) 

A port that is designed solely for power. It does not have digital logic to transfer photos or files.

• How it works: To tell the phone that it is a powerful charger, it simply „shorts“ the two data lines (D+ and D-) inside the port itself. When the phone „senses“ that D+ and D- are connected together, it knows that this is a DCP and can safely draw up to 1.5A of current at 5V.
• When it works: When you use devices that plug directly into a wall outlet or car cigarette lighter (old adapters, old and not so old power banks).

CDP (Charging Downstream Port) 

A much „smarter“ port. It allows your device (e.g. phone) to simultaneously charge quickly and be recognized by your computer as a data device (for file transfers, ADB debugging, etc.).

• How it works: The CDP contains specialized electronics. When you connect your phone, this port uses a complex series of signals on the data lines (D+/D-) to tell your phone, “I’m a USB data port, but I also have a powerful power supply. You can draw up to 1.5A while we talk.”
• When it works: When you’re testing the USB ports on a modern computer or an expensive docking station.

When the cable is smart: the E-Marker chip

I mentioned that some cables have a chip embedded in them. This is most often a microscopic chip embedded in one or both connectors of a USB Type-C to Type-C cable, and is called an E-Marker (Electronic Marker).

The E-marker can be likened to an “electronic ID” for the cable.

• What it is for: In the standard USB PD (Power Delivery) protocol without E-Marker, the charger is not allowed to deliver more than 3A of current (i.e. a maximum of 60W at 20V), so as not to overheat and ignite a thin or cheap cable.
• How it works: However, when the charger and the phone „talk“, they „ask“ the cable: „What are you?“.
  1. If the cable has an E-Marker, it responds digitally on the CC line: „I am a certified cable, I can withstand 5A of current and support USB 3.2 data.“
  2. Then the charger safely activates profiles from 60W to 100W (and even 240W in PD 3.1).

What about VOOC/SuperVOOC cables?

Some cables do not need E-Marker (for example, those from OPPO/OnePlus/Realme, which work on SuperVOOC protocols). They have their own proprietary chips. Their approach is different – in them the voltage is low (5V or 10.5V), but the current is significant (up to 6A-12A) to achieve the desired charging power.

• Different standard: E-Marker is an open standard of USB-IF. SuperVOOC is privately owned by OPPO. If the charger uses the PD protocol to „knock on the door“, the OPPO chip will not respond. That’s why the FNIRSI tester will write to you: „No E-Marker Found“.
• Hidden Hardware/Software: In older USB-A to USB-C cables for VOOC, recognition is often done in a purely hardware way – an additional, proprietary pin inside the USB-A connector that the phone detects. In modern OPPO USB-C to USB-C cables there is a chip, but it uses proprietary cryptographic keys to identify itself to the phone as „original“.

The original OPPO cable has a chip, but the PD protocol cannot read the information inside it because it is locked.

The difference in approaches (20V/5A vs. 10V/10A) 

• PD (Power Delivery): It uses high voltage (e.g. 20V) to transfer power. The chip (E-Marker) is needed to confirm that the cable can withstand high current (5A) so that it does not catch fire.
• SuperVOOC: It uses low voltage (5V or 10V) to transfer power, but with extremely high current (up to 6A-12A depending on the version). Here, the chip is not for voltage safety, but for authentication. OPPO wants to make sure that you are using their specific cable, which has thicker copper wires to transfer this high current without loss.

Most mass PD cables (without E-Marker), even if they are of good quality, cannot transfer 10-12A current at 5V-10V. The OPPO phone „knows“ this, „talks“ to the chip in the original cable and only then activates SuperVOOC. If the chip does not respond, the phone limits charging to the basic 5V/2A.

Systematizing the Jungle: A Table of Fast Charging Protocols

Here is my attempt to systematize the jungle in a table:

Conclusion

Please be lenient if there is a mistake somewhere – the jungle is a jungle for me too, although I am already quite successfully navigating. I will be happy to receive any constructive comments and additions – the comments are at your disposal!

Sources and useful information about the article

1. USB Implementers Forum (USB-IF):

   • Official technical specifications for USB Power Delivery (PD) 3.1, USB Type-C® Cable and Connector and Battery Charging (BC1.2) standards.

   • URL: https://www.usb.org/documents

2. Qualcomm Technologies, Inc.:

   • Technical information and overview of Quick Charge (QC) technology generations: QC 2.0, 3.0, 4, 4+ and QC 5.

   • URL: https://www.qualcomm.com/products/features/quick-charge

3. OPPO Global:

   • Official information about the patented VOOC and SuperVOOC fast charging technologies also used by the OnePlus brands and Realme.

   • URL: https://www.oppo.com/en/newsroom/press/oppo-supervooc-flash-charge/

4. Samsung Electronics:

   • Adaptive Support Information Fast Charging (AFC) in older models and the implementation of universal PD/PPS standards in new devices.

   • URL: https://www.samsung.com/global/galaxy/what-is-fast-charging/

5. Huawei Consumer BG:

   • Details of Huawei FastCharge Protocol (FCP) and SuperCharge Protocol (SCP) technologies.

   • URL: https://consumer.huawei.com/en/support/content/en-us00693997/

6. MediaTek Inc.:

   • Technical overview of the MediaTek Pump Express (PE) standard.

   • URL: https://www.mediatek.com/features/pump-express

7. FNIRSI Technology Co., Ltd.:

   • User manuals and specifications of the FNB58 and FNB-C2 USB testers used for diagnostics of the described protocols.

   • URL: https://www.fnirsi.com/download

Материалът Wandering through the jungle of fast charging protocols: Why „powerful“ isn’t always „fast“ е публикуван за пръв път на Галя и Тони - Галанто.

FNIRSI LCR-ST2 Master Class: A Practical Guide to Precise Measurements

Unlock the full potential of the FNIRSI LCR-ST2 Smart Tweezers with my practical tips and experience.

After going through the ins and outs of DeepVNA together, FTX-1F and FTDX10, it’s time to pay attention to a tool that has quickly become an indispensable assistant on my workbench – the FNIRSI LCR-ST2 smart tweezers.

This is my fourth book in the „Master Class“ series. In it, I decided to share not only dry technical data, but also real diagnostic methods that I use every day. In the world of miniature SMD components, a good tool is just the beginning. The real magic happens when you know how to decipher the „truth“ that the numbers on the screen are trying to tell you.

What will you find in this „Master Class“?

The manual is structured to take you from the first turn-on to the expert analysis of complex faults. In it I reveal:

• Dynamic Parameter Control: How to use the “hidden” joystick functions to see Q-factor, Impedance (Z) and phase shift directly on the main screen.
• Capacitor Diagnostics: My “Golden Rule” for measuring ESR (Rs) at 100kHz and why capacitance is often not the most important metric.
• Short Circuit Locator: The milliohm technique I use to find a blown component on a power rail without unsoldering everything.
• Frequency Analysis (SCAN): How to understand the behavior of coils and transformers in real operating conditions.

“Where “Numbers meet truth” is the motto for this guide.

My goal is to give you confidence in every measurement you make.

This book is the perfect complement to my previous „Master Classes“ for DeepVNA, FTDX10 and FTX-1F for practicing radio amateurs.

Download the book in PDF format

You can download the full version of the book „FNIRSI LCR-ST2 MASTER CLASS Complete guide to precise measurements with LCR-ST2“ completely free of charge from the link below:

[Download PDF: FNIRSI LCR-ST2 MASTER CLASS – LZ3AI]

Support the shared experience

„This manual is my contribution to the amateur radio community and will always be free to share. If the information in it was useful to you and you want to express your support for my work, you can buy me a cup of virtual coffee via the link below. Any such recognition motivates me to continue sharing practical advice and new ones on the site. Thank you and 73! “ — Tony, LZ3AI

Friends, creating these guides takes hundreds of hours of testing, researching, and describing every feature. If you find my work useful and it has helped you save time or solve a difficult repair, you can express your gratitude and support my future projects. Your support is the „fuel“ that gives me the strength to continue sharing knowledge with the amateur radio community.

Buy me a coffee

Your feedback is important!

Amateur radio is a hobby of shared experience. Do you use different settings for your device? Do you have a „secret recipe“ for easily measuring different components without removing them from the board?

I would be glad if you share your opinions, corrections or personal settings in the comments below the article or over a cup of coffee. Let’s make this guide even more useful for the amateur radio community!

73 and see you on the air!

Tony, LZ3AI

About the author (LZ3AI): „I believe that sharing experience is the basis of the amateur radio movement. My „Master Classes“ focus on the practical side of things to help you get the most out of your equipment.“

Literature and sources used

In preparing this „Master Class“ I relied on:

• FNIRSI Technology Co., Ltd. – Official documentation and specifications of firmware v1.5.1.
• H. W. Ott – “Noise Reduction Techniques in Electronic Systems”.
• Galanto Electronic Library – Materials for ESR diagnostics and internal resistance of batteries.
• Personal laboratory practice – Dozens of hours of tests with reference components.

Материалът FNIRSI LCR-ST2 Master Class: A Practical Guide to Precision Measurements е публикуван за пръв път на Галя и Тони - Галанто.

Car Leakage Current

Typical values for leakage current (idle consumption) from a modern car battery are between 20 and 50 milliamperes (mA).

Normal and maximum permissible values

• Ideal value: Anything below 50 mA is considered completely normal for most gasoline and diesel cars. This energy is needed to maintain the memory of various modules such as the engine computer (ECU), the radio, the alarm system and others. Some experts claim that values below 20 mA should be considered normal. Here, the approach should be the same as with people. Each car is unique and it would be good to take this value into account when it is new so that it can be controlled. If its value is not known when it is new, the general rule is followed.
• Maximum permissible value: As an upper limit, a value of up to 80-85 mA is usually accepted. Although higher, this consumption should not cause ignition problems unless the car is not driven for several weeks.

When to worry?

You should look for the cause of the leak if the idle consumption is permanently above 85-100 mA. At such values, you risk your battery draining significantly faster, especially at lower temperatures or if the car is not driven daily. Values above 100 mA will almost certainly lead to starting problems after a few days of standstill.

How is leakage measured?

To measure the leakage current, you need a multimeter with the ability to measure direct current (amperes). The procedure in brief is as follows:

1. Turn off all consumers in the car (lights, radio, air conditioning, USB devices in the cigarette lighter).
2. Close all doors, but ensure access to the battery. In some cars, it is necessary to „trick“ the mechanism of the front hood or trunk into being closed (or the tailgate, rear door – depending on the location of the battery).
3. Wait about 30-40 minutes. This time is necessary for all electronic modules in the car to „fall asleep“. Do not start disconnecting the battery terminal before the measurement itself. It is possible that the lack of power during the waiting period may disrupt the normal „fall asleep“ of one of the electronic modules.
4. Connect the multimeter in series to the negative terminal of the battery. This means disconnecting the negative cable from the terminal and connecting the multimeter between the cable and the terminal itself. If the battery is in the trunk or under the back seat, find it and measure directly on it. In such cases, do not be fooled into measuring values at the terminals near the engine. The problematic leak may be exactly in the area between the battery and these terminals.
5. Read the value in milliamperes.

Probable causes

If you find a higher than normal consumption, the most common culprits are non-factory or damaged alarms, damaged or additionally installed audio systems or other electronic devices, defective relays, USB devices in place of the cigarette lighter or one of the electronic modules that does not „go to sleep“ properly. In such a case, it is best to contact a specialized service for diagnostics.

If you have experience in identifying and eliminating a leak, please share more details – make and model, causes and methods of elimination, in a comment. You will certainly help many people.

Материалът Leakage current in the car е публикуван за пръв път на Галя и Тони - Галанто.

Internal resistance of the car battery

Internal resistance (Ri​) is one of the most important indicators of the „health“ of the battery. FNIRSI HRM-10 is one of the measuring devices that can give a very good idea of the condition of a battery.

In short: the lower the internal resistance, the better the condition of the battery. Over time and use, it increases, which limits its ability to deliver high starting current.

Does the type of battery matter?

Yes, it matters a lot. The same table cannot be used for lead-acid, gel (GEL), AGM, EFB and lithium-ion (Li-ion) batteries. Each type has a different chemistry and internal structure, which leads to completely different internal resistance values.

Therefore, it is impossible to create a universal table for all types. Below are indicative tables for the most common types.

Important: For the most accurate assessment, always compare the measured value with the specifications of a brand new battery of the same model, if available. A more reliable method is to monitor how the resistance of your battery increases over time. A 50-100% increase in resistance from its original value is usually a sure sign that the battery is nearing the end of its life.

12V Automotive Battery Chart (Lead Acid: EFB, AGM)

For automotive batteries, it is more practical to relate the internal resistance to the cranking current (CCA – Cold Cranking Amps) rather than the capacity (Ah). More powerful batteries with a higher CCA have lower internal resistance.

Table for Small Lead Acid Batteries (SLA/VRLA)

These are encapsulated batteries, often used in UPS devices, alarm systems, strollers, etc.

Lithium-ion (Li-ion/Li-Po) Battery Table

There is a huge variety here, but here are some general guidelines. „Power“ cells (for high current, e.g. in screwdrivers) have lower resistance than „Capacity“ cells (for high capacity, e.g. in laptops).

How to interpret the results?

1. Charge the battery: Always test a fully charged battery. At low charge the internal resistance is higher and will mislead you.
2. Temperature: Measure at room temperature (20-25°C). At lower temperatures, the resistance increases.
3. Good contact: Make sure the clamps of the device make clean and solid contact with the battery terminals. Oxidation or contamination can distort the result.

Please share your experience in a comment. It will be interesting for everyone.

Материалът Internal Resistance of the Car Battery е публикуван за пръв път на Галя и Тони - Галанто.

The secret to long life: How to tell whether the battery is excellent, good or damaged by measuring internal resistance

Internal resistance is one of the best indicators of the condition of a battery. It is like blood pressure for a person – it gives a lot of information about its “health”. Let’s take a closer look at how we can use internal resistance to assess the health of different types of batteries.

What is internal resistance?

The internal resistance (R_int​) of a battery is a measure of the resistance of all the components inside it that impede the flow of electric current. This includes the resistance of the electrolyte, the electrodes, the separator, and the connections between them. The lower the internal resistance, the more efficiently the battery can deliver and receive energy.

Why is it important?

Over time and use, the internal resistance of a battery increases. This is due to various processes such as:

• Electrode wear: Formation of layers with higher resistance, change in crystal structure.
• Electrolyte degradation: Increase in viscosity, decrease in ionic conductivity.
• Loss of active material: Contraction and expansion leading to loss of contact.

Increased internal resistance leads to:

• Reduced capacity: The battery cannot store as much energy.
• Reduced power: It cannot deliver high current, especially under continuous load.
• Increased heating: More energy is lost as heat during charging and discharging.
• Faster self-discharge: Not directly related, but often goes hand in hand with other degradation processes.

How is internal resistance measured?

There are two main measurement methods:

1. AC (alternating current) method: This is the most common and accurate method. The device applies a small alternating current of a certain frequency (for example, 1 kHz) through the battery and measures the voltage drop. Internal resistance is calculated using Ohm’s law (R=V/I). Most specialized battery testers use this method.
2. DC (direct current) method: The voltage drop when a known load is applied is measured. This method is simpler, but less accurate, as it depends on the state of charge and temperature. However, it is more accessible in practice, because it does not require specialized devices – two multimeters and a sufficiently powerful resistor with accurate resistance are sufficient (for example). There are very good descriptions of this method on Youtube.

Classification of batteries by internal resistance

It should be borne in mind that there are no universal, strictly defined values ​​of internal resistance that are applicable to absolutely all batteries, as they depend on:

• Chemical composition: Li-ion, LiFePO4, NiMH, lead-acid have different typical values.
• Capacity: A battery with a higher capacity usually has a lower internal resistance.
• Size/Form factor: 18650, 21700, 26650 have different designs and sizes.
• Manufacturer: Different manufacturers and series have differences.
• Purpose: Batteries for high currents (power cells) have a much lower internal resistance than those for high capacity (capacity cells).
• Temperature: At lower temperatures, the internal resistance increases.
• State of charge (SoC): At very low or very high charge the internal resistance may increase slightly. For the most accurate measurements, it is recommended that the battery be about 50-80% charged.

Guidelines

The following are guidelines for determining the quality of different types of batteries.

Lithium-ion batteries (18650, 21700, 26650, etc.)

These batteries are very sensitive to internal resistance. Values ​​are often measured in milliohms (mΩ).

Table with updated indicative values ​​for 18650/21700 according to purpose

Internal resistance of lithium „coin“ batteries (CR2032, CR2016, CR2025, etc.)

These batteries are of the type primary lithium batteries (non-rechargeable). Their chemical composition is different (lithium-manganese dioxide usually) and they are designed for very low discharge current for an extremely long period (years).

• Intended use: Watches, computer motherboards (CMOS batteries), small remotes, toys, low-power medical devices.
• Typical internal resistance: The internal resistance of these batteries is significantly higher than that of rechargeable lithium-ion batteries, but this is normal for their purpose.

Important notes about „coin“ batteries:

• High sensitivity of the meter: Some internal resistance testers, especially those designed for Li-ion batteries, may not give accurate or reliable readings for coin batteries due to their very high impedance and different frequency characteristics.
• Focus on voltage: With these batteries, it is often more practical to relies on measuring the voltage under minimal load, as it drops significantly as the battery nears the end of its life. A new CR2032 is around 3V, while below 2.8V is already considered worn out for most applications. However, internal resistance is a better indicator of remaining life than open circuit voltage alone.
• They are not for high current: Trying to draw high current from such a battery would result in a huge voltage drop due to the high internal resistance.

Differences in internal resistance according to the purpose of lithium-ion batteries

Lithium-ion batteries of the same form factor (e.g. 18650) are manufactured for different purposes, which directly affects their internal resistance:

1. Power Cells:
   • Purpose: Power tools, vaping devices, drones, electric bicycles/scooters – applications where it is necessary to deliver high currents for a short or long period.
   • Design: Optimized for minimal internal resistance through thinner separators, larger electrode area, and higher conductivity materials. This is usually at the expense of capacitance.
   • Typical internal resistance (new): Very low, typically below 15 mΩ, often in the 8−12 mΩ range.
2. High Capacity Batteries (Capacity Cells):
   • Intended Use: Laptops, flashlights, power banks, medical devices – applications where maximum capacity is important, not so much the ability to deliver very high current.
   • Design: Optimized for maximum capacity through a larger amount of active material. This can lead to slightly higher internal resistance compared to „power“ cells.
   • Typical internal resistance (new): Moderately low, usually in the 20−30 mΩ range, although some newer and more efficient models can be below 20 mΩ.
3. Low Drain / Long Life Cells:
   • Use: Applications where very low, constant current is required for a long period of time, such as watches, remote controls, sensors, backup batteries.
   • Design: The focus is on voltage stability, low self-discharge and long life at low loads. Internal resistance is not as critical a factor as with „power“ cells, but should still be within acceptable limits.
   • Typical internal resistance (new): Higher than „power“ and „capacity“ cells, but still within reasonable limits for lithium-ion technology. For 18650 or similar cells, values ​​of 40−60 mΩ for new cells designed for very low current only can be considered normal. Important: Values ​​above 100 mΩ for 18650 even for this type will indicate degradation.

Additional notes for Li-ion batteries:

• New batteries: Will always have the lowest internal resistance.
• Parallel connected: With parallel connected cells it is critical that they all have similar internal resistance to balance the load and prevent overloading of the weaker cells. With such a connection, the total resistance is lower (calculated as with parallel resistors) and, accordingly, they can deliver more current at the same voltage.
• LiFePO4 (Lithium Iron Phosphate): These batteries usually have a lower internal resistance than standard Li-ion, especially when they are designed for high currents. For example, a new LiFePO4 32650 battery may have an internal resistance of less than 5 mΩ.

• Get batteries from manufacturers that guarantee a certain internal resistance in their specifications. Avoid battery „repackers“, no matter how much they praise them in forums and reviews. The claim that 200 mΩ can be a good internal resistance for an 18650 is false – this is too high a value even for low-current batteries. At 200 mΩ, an 18650 battery, regardless of its purpose, would be severely degraded and with very limited capacity and power, practically unusable.

Nickel-Metal Hydride (NiMH) and Nickel-Cadmium (NiCd) batteries

These batteries usually have a higher internal resistance than lithium-ion, especially in smaller sizes (AA, AAA).

Additional notes for NiMH/NiCd:

• „Memory effect“ and crystallization: These effects can increase internal resistance.
• The discharge-charge limits during initial operation are important due to the memory effect.

Lead-acid batteries (car, some stationary, etc.)

In car batteries, the internal resistance is extremely low and is measured in microohms (μΩ) or tenths of a milliohm (mΩ). It is a key indicator of the battery’s ability to deliver high cranking current (CCA – Cold Cranking Amps).

Additional notes for lead-acid batteries:

• State of charge: In these batteries, the state of charge has a significant impact on the internal resistance. Measurements should be made with a fully charged battery.
• Temperature: At low temperatures, the internal resistance increases significantly, which is the cause of difficulties when starting a car in winter.
• Sulfation: This is the main cause of increased internal resistance in lead-acid batteries.

General advice and conclusions

• Measure with the same device: To obtain the most reliable results, always use the same internal resistance tester. Different devices may give slightly different readings.
• Consistency: Measure under similar conditions – temperature and state of charge (for Li-ion around 50-80%, for lead-acid fully charged).
• Combine with other indicators: Internal resistance is an excellent indicator, but it is not the only one. Combine it with capacity measurement (especially for Li-ion), voltage under load and visual inspection (for swelling, leaks, etc.).
• Track the development: The best assessment of the condition of the battery is obtained when you track its internal resistance over time. If it starts to increase rapidly, this is a sure sign of degradation.
• Unit of measurement: Be careful with the units of measurement – ​​milliohms (mΩ) and microohms (μΩ). 1 mΩ=1000μΩ.

Using the FNIRSI HRM-10: Practical Aspects

FNIRSI HRM-10 is a popular and relatively affordable battery internal resistance tester, and with it we can easily practically understand whether the battery is excellent, good or damaged.

It uses the AC (alternating current) method at 1 kHz, which is a standard and reliable approach to measuring the internal resistance of batteries. Importantly, it is a four-wire (Kelvin) tester, which is key to accuracy. Four-wire measurement eliminates the influence of test lead resistance and battery terminal contact, which is a major source of error in simpler two-wire methods.

Overall, you can expect the FNIRSI HRM-10 to provide fairly accurate and reliable results for its price, especially for 18650, 21700, 26650 lithium-ion batteries, as well as automotive batteries.

It is recommended to consider the following features to be sure whether the battery is excellent, good or damaged:

1. Accuracy at extreme values:
   • Very low resistances (below 1 mΩ): Although the HRM-10 is quite good at measuring the internal resistance of new, high-quality car batteries (which can drop below 2-3 mΩ), there may be slight deviations from ideal laboratory instruments. However, for everyday use and condition determination, a difference of 0.1−0.2 mΩ will not be fatal.
   • Very high resistances (above 1-2 ohms): Although it can measure up to 200 ohms, with coin batteries (CR2032 and similar), whose resistance can be hundreds of milliohms to a few ohms, the results may be less stable or vary more. This is not a problem with the device specifically, but with the specificity of these batteries and the fact that testers are optimized for lower values.
2. Calibration: Although the FNIRSI HRM-10 comes factory calibrated, over time or under extreme conditions of use, the accuracy may shift slightly. The device has the ability to be calibrated, which is a plus. For maximum accuracy, periodic checking with a known precision resistor (or other calibrated device) would be very useful.
3. Temperature: As mentioned, temperature has a strong effect on internal resistance. Make sure the batteries you are testing are at room temperature (around 20−25∘C) for the most consistent and comparable results. If you are testing a battery that has just been used heavily (and is warmed up) or has been in the cold, the results will be distorted.
4. State of Charge (SoC): Although the AC method is less sensitive to SoC than the DC method, it is still advisable to test Li-ion batteries at a similar state of charge (e.g. 50−80%). Lead-acid batteries must be fully charged for an adequate assessment.
5. Terminal Contact: Although it is a four-wire, poor contact between the probes/clamps and the battery terminals can lead to inaccurate and/or variable readings. Make sure the terminals are clean and you have a solid, tight contact.
6. „Noise“ in the measurement: In some cases, especially with lower internal resistance values ​​or in the presence of interference, slight fluctuations in the readings may be observed. This is normal for most handheld devices. The approach in this case is to take several measurements and average the results if necessary.

Overall impressions of FNIRSI HRM-10:

• Advantages:
  • Four-wire method (Kelvin connection): Excellent basis for precise measurements.
  • 1 kHz AC measurement: Industry standard.
  • Wide range: Allows testing of various types of batteries – from small lithium-ion to automotive.
  • Sorting function: Allows you to set thresholds for „good“ and „bad“ batteries, which is very useful for sorting large numbers of cells.
  • Price/performance: Offers very good functionality for its price range.
• Disadvantages (usually minor):
  • May require a little time to get used to the menus.
  • As with any device, there may be slight variations between individual units.

Conclusion

FNIRSI HRM-10 is a very good choice for practical use. The theory we discussed is fully applicable to its measurements. Do not expect significant differences that would make the theory meaningless, but you should also be aware of the factors that can affect the accuracy of the measurement (temperature, SoC, contact) and minimize them according to your capabilities and circumstances to get the most reliable results.

If you follow these basic rules, the FNIRSI HRM-10 will be an extremely useful tool for assessing the condition of batteries and will help you make informed decisions about which ones are still usable and which ones should be discarded.

Last words

All data from this article is only a starting point. It is recommended to collect data from one’s own practice and real experience of trusted people from the amateur radio community about the internal resistance and capacity of batteries, from which to draw conclusions about their quality. User reviews, unless supported by real measurements, are not the best source for an informed decision.

According to my experience so far, batteries should only be purchased from manufacturers who are not afraid to publish real data about their batteries. The so-called „repackers“, if they publish any specifications at all, they are unrealistic and often obviously fake, but with a tempting price. But there is no guarantee that if their batteries are more expensive, they are of better quality.

Whether the battery is excellent, good or damaged?

We hope that this research of mine was useful to you and I will be glad to share your opinion in the comments, no matter what it is.

Материалът Whether the battery is excellent, good or damaged? How to tell by measuring internal resistance е публикуван за пръв път на Галя и Тони - Галанто.