Lead acid batteries are typically used in the automotive industry, where they provide a high current pulse to start the vehicle, in traction applications, where they undergo periodic deep discharge and charge, and in stationary applications, where they remain in charged state most of their life. They are used also in hybrid electric vehicles (HEVs) and in remote area power supply systems (RAPS), where they remain in a state of about 50% of charge during their operation. In this state, these batteries can be charged or discharged with high effectivity. In all these applications, it is necessary to monitor and report the battery state of charge (SoC) instead of simply monitoring the battery voltage.