In an environment where there is no major breakthrough in lithium battery technology and new energy batteries have not yet been applied to electronic products, the battery life problem has always plagued the majority of mobile phone users. The emergence of fast charging technology allows users to charge more power to their phones in fragmented time. The battery life problem can be solved from another aspect. But there are still many netizens who mistakenly think that fast charging heads are interchangeable. Today the author brings you 2 experiments: 1. Verify the compatibility of fast charging mobile phones/charging heads; 2. The speed performance of charging iPhone 6s with a non-original charger.

Measurement method

‌Direct Current Internal Impedance Method (DCIR)‌

Fully charge the battery to a specific SOC (e.g., 100%).

Discharge at a constant high current (e.g., 40A-100A) for a few seconds.

Records the open circuit voltage before discharge (U1) and the voltage at discharge (U2).

Calculate internal resistance: r = (U1 - U2) / I.

‌Principle: Apply a short-term high-current pulse to the battery, measure the instantaneous change in voltage, and calculate the internal resistance according to Ohm's law.

‌Steps‌：

‌Pros:: The principle is simple, and the results are intuitive.

‌Cons:: The measurement process may cause minor damage to the battery and is affected by the contact resistance.

‌Alternating Internal Resistance Method (ACIR)‌

Use a dedicated AC internal resistance testeror Electrochemical workstation‌。

Connect the test fixture to the positive and negative terminals of the battery.

The instrument automatically injects an AC signal and measures the impedance, usually directly displaying the internal resistance value in milliohm mΩ.

‌Principle: A tiny AC signal is applied to the battery, the AC voltage response it produces is measured, and the internal resistance is calculated by impedance.

‌Steps‌：

‌Pros:: Fast and non-destructive measurement, suitable for online monitoring and production line sorting.

‌Cons:: The cost of the equipment is high, and the results may be affected by the frequency of measurements.

Notes:

‌Safety first: Be sure to operate within the rated voltage range of the battery to avoid short circuits.

‌Method selection: The DC method is suitable for laboratory or in-depth testing; The AC method is suitable for rapid screening or routine maintenance of production lines.

‌Interpretation of the results: The smaller the internal resistance, the better the battery performance is usually better. The internal resistance of new batteries ranges from a few milliohms to tens of milliohms, depending on the battery type and capacity. The increase in internal resistance is a sign of battery aging.

‌Standardization trends: The industry is promoting the standardization of internal resistance measurement to ensure data comparability and support battery cascade utilization.

Tool recommendation

‌Basic measurements: Digital multimeters (resistance files) can be roughly compared, but the accuracy is limited.

‌Professional measurement: Recommended Battery internal resistance tester(such as Hioki, Huayi and other brands) or Electrochemical workstation, they provide more accurate and reliable DC or AC internal resistance data.