It does not require the battery to be at rest to perform an accurate measurement. Unlike the OCV method, this method is able to determine the evolution of the state of charge during battery use. This integration directly gives the quantity of electrical charges injected or withdrawn from the battery, thus making it possible to precisely quantify the SoC of the battery. To track the state of charge when using the battery, the most intuitive method is to follow the current by integrating it during cell use. Lithium Iron Phosphate Calibrated SoC meter 2/ SoC estimation using Coulomb Counting method A precise measurement, coupled with a modelled load curve, allows SoC measurements to be obtained with an accuracy of 10 to 15%. However, calibrated charge indicators can be used specifically for lithium-ion batteries in general and lithium iron phosphate batteries in particular. The diagram below shows that the voltage measurement difference between a DoD value of 40% and 80% is about 6.0V for a 48V battery in lead-acid technology, while it is only 0.5V for lithium-iron phosphate ! Lithium vs AGM Soc estimation by OCV method Indeed, the voltage difference between two SoC values may be so small that it is not possible to estimate the state of charge with good precision. Lithium Iron Phosphate technology has the flattest discharge curve, which makes it very difficult to estimate SoC on a simple voltage measurement. However, Lithium-ion batteries have a much flatter discharge curve, which means that over a wide operating range, the voltage at the battery terminals changes very slightly. It can be seen that lead-acid batteries have a relatively linear curve, which allows a good estimation of the state of charge : for a measured voltage, it is possible to estimate fairly precisely the value of the associated SoC. As an example, the diagram below compares the discharge curves between a lead battery and a Lithium-Ion battery. This relationship between voltage and SOC depends directly on the battery technology used. The voltage will be highest when the battery is fully charged and lowest when it is empty. We will detail here the two most common and simplest methods to estimate the state of charge of a battery : voltage method or Open Circuit Voltage (OCV) and coulomb counting method.ġ/ SoC estimation using Open Circuit Voltage Method (OCV)Īll types of batteries have one thing in common: the voltage at their terminals decreases or increases depending on their charge level. Some methods are quite complicated to implement and require complex equipment (impedance spectroscopy or hydrometer gauge for lead acid batteries). There are several ways to get Lithium-Ion State of Charge (SoC) measurement or Depth of Discharge (DoD) for a lithium battery. Lithium-Ion State of Charge (SoC) measurement Modular lithium battery pack (voltage up to 700v) Scalable Lithium-Ion Energy Storage System

PowerStart 12V Starter Battery – 600CCA.

Analog rv battery monitor