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For Manganese Lithium (ML) cells, the maximum number of charge/discharge cycles (cell life) is affected by the depth of discharge (DoD). This calculator estimates ML cell lifetime based upon a given depth of discharge. The calculator uses an estimated cell load to determine approximate backup time versus discharge depth.
As a ML cell is cycled, the capacity at full charge decreases. This means that that it will take less time to reach a given depth-of-discharge as the cell is cycled. This calculator does not take into account the reduced capacity during use, but is intended to serve as a first approximation of cell life.
This calculator models the charge/dischage cycles versus dischage depth using the formula y = (a+b*x)/(1+c*x), or cycles = (a+b*DoD)/(1+c*DoD) where a, b, and c are constants based upon cell test data. Hours to the discharge depth are calculated using the formula y = (a+b*(Depth of Discharge)) / (1+c*(Depth of Discharge)) Total hours are calculated by multipling hours by the number of cycles.
Where the inputs are:
- IBAT--The current drawn by the device when powered by the battery supply input.
- DoD--Depth of Discharge. The amount of cell discharge as a percent of total capacity.
For details on the formulas used in the calculations, refer to application note 3779.
ML Cell Charge/Discharge Cycles vs. Depth of Discharge Figure 1.
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