Depth of Discharge (DoD) is an alternative method for evaluating the state of charge( SoC) of rechargeable batteries. Depth of Discharge identifies the amount of energy that has been removed from a battery. It forms the counterpart to the state of charge. Both values are inversely related to each other and add up to 100%: if one value rises, the other falls and vice versa.
The DoD value refers to the fully charged state. In this state, the DoD value is 0 %, the SoC value 100 %; in totally discharged state, the DoD value is 100 %, the SoC value 0 %. The Depth of Discharge value can also be expressed in ampere-hours. Since rechargeable batteries can be charged beyond their nominal capacity, the DoD value can also assume values of over 100 %.
The degree of discharge of rechargeable batteries depends on the battery technology and influences the battery life, which depends on the state of charge range in which the battery is operated. For lithium-ion batteries, the most favorable range is at a relatively high state of charge between 10% and 80%; the situation is different for lead batteries, whose most favorable operating range is at a state of charge above 60%.
Battery life is also dependent on Depth of Discharge. There is a non-linear relationship between the two. The higher the DoD value becomes, the shorter the battery life. At the same time, as the Depth of Discharge increases, the number of battery charges and discharges decreases because the battery is subjected to greater chemical and mechanical stress. By limiting the DoD values in the applications, the battery life can be significantly extended. The depth of discharge can be monitored by the battery management system and adjusted according to the aging state of the battery.