>From battery university http://batteryuniversity.com/learn/article/how_to_know_end_of_battery_life Some lithium-ion batteries have a very flat discharge curve and the voltage method does not work well to provide SoC in the mid-range. An innovative new technology is being developed that measures battery SoC by magnetic susceptibility. *Quantum magnetism *(Q-Mag=99) detects magnetic changes in the electrolyte and plates that correspond to state-of-charge. This provides accurate SoC detection in the critical 40-70 percent mid-section. More impotently, Q-Mag=99 allows measuring SoC while the battery is being charged and is under load. The lithium iron phosphate battery in Figure 3 shows a clear decrease in *relative magnetic field units* while discharging and an increase while charging, which relates to SoC. We see no rubber band effect that is typical with the voltage method in which the weight of discharge lowers the terminal voltage and the charge lifts it up. Q-Mag=99 also permits improved full-charge detection; however, the system only works with cells in plastic, foil or aluminum enclosures. Ferrous metals inhibit the magnetic field. [image: Magnetic field measurements of a lithium iron phosphate during charge and discharge] *Figure 3: Magnetic field measurements of a lithium iron phosphate during charge and discharge* Relative magnetic field units provide accurate state-of-charge of lithium- and lead-based batteries. Courtesy of Cadex (2011) Q-Mag=99 also works with lead acid. This opens the door to monitor starter batteries in vehicles. Figure 4 illustrates the Q-Mag=99 sensor installed i= n close proximity to the negative plate. Knowing the precise state-of-charge at any given moment optimizes charge methods and identifies battery deficiencies, including the end-of-battery-life with on-board capacity estimations. [image: Q-Mag=99 sensor installed on the side of a starter battery] *Figure 4: Q-Mag=99 **sensor installed on the side of a starter battery* The sensor measures the SoC of a battery by magnetic susceptibility. When discharging a lead acid battery, the negative plate changes from lead to lead sulfate. Lead sulfate has a different magnetic susceptibility than lead, which a magnetic sensor can measure. Courtesy of Cadex (2009) Q-Mag=99 is also a candidate to monitor stationary batteries. The sensing mechanism does not need to touch the electrical poles for voltage measurements and this poses an advantage for high-voltage batteries. Furthermore, Q-Mag=99 can assist EVs by providing SoF accuracies not possib= le with conventional BMS. Q-Mag=99 may one day assist in the consumer market t= o test batteries by magnetism. It is conceivable that one day an iPhone or iPad can be placed on a test mat, similar to a charging mat, and read battery SoC and performance. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .