66 Also, acoustic emissions-monitoring systems can be used to listen for sounds generated by stress or cracking within the battery pack, providing an early warning of structural failures in predictive maintenance applications. As battery designs continue to diversify, leak testing systems have to keep up while offering greater precision and reliability. Under pressure Advanced air-pressure differential decay testers can measure larger ranges of volume and pressure, and cancel out the noise of factory environments to improve the accuracy and reliability of in-line testing. One of the latest systems features a differential sensor with a range of 20 pascals (Pa) and sufficient sensitivity to detect pressure variations as small as 0.001 Pa. Using a controlled air-injection process, this system pressurises the battery and a reference element. Once the target pressure is reached, the pressurisation stops, allowing the system to analyse pressure variations and accurately determine the leakage rate in millilitres per minute. The system’s software enables users to monitor the entire pressurisation cycle, continuously track leakage rate during the test, and optimise testing parameters. Testing battery components quickly is critical in production, and one innovation in this area is the measurement of discharge current to detect small holes in plastic parts, such as pouch cells. The method works by applying a high voltage to a sharp probe that is brought close to an earth-connected base supporting the cell under test. If there is a hole in the cell, ions will start moving from the earth to the sharp end of the probe, resulting in loss of power, and this will be interpreted as a leak. The pass/fail decision is based on the measured percentage of the cell’s nominal voltage, which reflects the discharge current. While this does not quantify the leak rate, the developer claims it is the fastest ever device to detect a leak in a go/no-go process, achieving cycle times of under 0.7 s. Most battery packs feature vent valves with permeable membranes that allow gas and vapours to pass through while sealing the pack against water ingress. This can make it difficult to test the seal between the pack housing and the vent valve, but in one recent innovation a feature that enables leak checks is integrated into the valve to allow sealing to be tested after the valve is installed. This supports testing during manufacture, as well as in maintenance and repair. In the company’s own tests, it says, the filling of a battery pack with 120 litres of free air volume has been achieved in less than 5 s. Getting specific Detection and identification of specific gases is improving with the application of techniques such as colour-changing chemical reagents and a reactive gas, and refinements to instruments based on mass spectrometry. The colorimetric chemical technique is a recent innovation, taking advantage of the fact that, like all chemicals, new compounds that form when two or more molecules meet have unique molecular structures that absorb light differently, giving them specific colours. Creating a leak detection system depended on selecting a safe combination of reactive ‘challenge’ gas and colour-changing chemical reagents. The technique works by first placing the colour-change reagent over the welded or sealed areas on the outside of the battery enclosure and then pumping the challenge gas into the enclosure at low pressure. As the gas diffuses thorough the case, it reveals and permanently marks any leak points. The most critical task in developing the system was finding the right combination of challenge gas and colour-change reagent, both of which had to be Product focus | Battery leak testing March/April 2025 | E-Mobility Engineering Designed for large components such as EV battery housings, the F670LV from ATEQ features Differential Noise Cancelling (DNC) technology to compensate for background disturbances (Image courtesy of ATEQ) Permeable membranes allow gas and vapours to pass through while sealing the pack against water ingress
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