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Depth of discharge (DoD) is an important parameter appearing in the context of rechargeable battery operation. Two non-identical definitions can be found in commercial and scientific sources. The depth of discharge is defined as: the maximum fraction of a battery's capacity (given in Ah) which is removed from the charged battery on a regular basis.
For example, consider a battery with a capacity of 200 Ah at the C 20 rate (C 20 means the 20-hour rate – i.e. the rate that will fully discharge the battery in 20 hours – which in this case is 10 A). If this battery is discharged at 10 A, it will last 20 hours, giving the rated capacity of 200 Ah.
Depth of discharge (DOD) is normally stated as a percentage of the nominal ampere-hour capacity; 0% DOD means no discharge. As the usable capacity of a battery system depends on the rate of discharge and the allowable voltage at the end of discharge, the depth of discharge must be qualified to show the way it is to be measured.
In a battery electric vehicle (BEV), the state of charge indicates the remaining energy in the battery pack. [4] It is the equivalent of a fuel gauge.. The state of charge can help to reduce electrical car's owners' anxiety when they are waiting in the line or stay at home since it will reflect the progress of charging and let owners know when it will be ready. [5]
For example, for a battery with a capacity of 500 mAh, a discharge rate of 5000 mA (i.e., 5 A) corresponds to a C-rate of 10C, meaning that such a current can discharge 10 such batteries in one hour. Likewise, for the same battery a charge current of 250 mA corresponds to a C-rate of C/2, meaning that this current will increase the state of ...
The relationship between the Ah capacity and the discharge rate is not linear; as the discharge rate is increased, the capacity decreases. A battery with a 100 Ah rating generally will not be able to maintain a voltage above 10.5 volts for 10 hours while being discharged at constant rate of 10 amps. Capacity also decreases with temperature.
The empirical relationship between discharge rate and capacity is known as Peukert's law. When a battery is charged or discharged, only the reacting chemicals, which are at the interface between the electrodes and the electrolyte, are initially affected.
By 2007, monthly self-discharge rate was estimated at 2% to 3%, and 2 [6] –3% by 2016. [68] By comparison, the self-discharge rate for NiMH batteries dropped, as of 2017, from up to 30% per month for previously common cells [69] to about 0.08–0.33% per month for low self-discharge NiMH batteries, and is about 10% per month in NiCd batteries.