Depth of discharge

Depth of discharge (DoD) is the percentage of a battery's capacity that has been taken out, measured against the fully charged state. DoD and state of charge always add up to 100 percent. For example, a battery discharged once a day down to 65% of its capacity has a DoD of 35%. The allowable DoD is the deepest discharge permitted in operation. For deep-cycle batteries it is usually held to no more than 75 to 80%, and it must also be limited to keep lead-acid batteries from freezing in very cold conditions. Charge controllers and battery-based inverters enforce the DoD limit with a low-voltage disconnect set point. For a typical lead-acid cell, an LVD of 1.85 to 1.91 volts per cell corresponds to a DoD of 70 to 80% at discharge rates of C/20 and lower. Battery life depends mainly on DoD, cycle count, time spent at each state of charge, and temperature. The link between DoD and life is non-linear, and a shallower daily DoD usually means a longer life. Together with battery capacity and daily load, the allowable DoD sets the days of autonomy for off-grid designs. For example, a 400 Ah bank used to 75% DoD gives 300 Ah of usable capacity. Monitoring systems and set points should keep the battery above its minimum state of charge. Some products, such as the SolarEdge Home Battery, claim full DoD with no 5% manufacturer energy reserve, and also offer a backup reserve setting.

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• sentence 7: support check: partial - Monitoring/set points avoiding minimum SOC and the SolarEdge no 5% reserve claim are stated, but the 'offers a backup reserve setting' is only implied by the diagram. -->