In recent years, lithium ion batteries have become wide-spread energy sources for various battery-powered applications. In particular, LiFePO₄ batteries are increasingly used for high-power automotive and storage applications. Unfortunately, the state of charge (SOC) is not uniquely determined by measuring just the LiFePO₄ battery's open-circuit voltage. However, an alternative approach for SOC determination is introduced by investigating the battery's magnetic susceptibility. This is motivated by the iron atom's magnetic state in the LiFePO₄ cathode material, which changes during charging and discharging. The magnetic susceptibility of differently charged battery samples will be investigated to correlate the magnetic moment with the SOC in view of a new sensor concept.