Grading cells for a battery pack
AssigneeWilson Greatbatch Technologies, Inc.
InventorsSteven Davis, Esther S. Takeuchi
Life of this patent
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Abstract
A battery pack having a first secondary cell and a second secondary cell, preferably of a non-aqueous chemistry, is described. Each secondary cell has a discharge capacity and an internal resistance to a direct charge current. To diminish and alleviate problems associated with extended cycling of battery packs, the internal resistance to the direct charge current and the discharge capacity of each secondary cell is substantially matched. Thereby, the battery packs have longer running voltages and increased energy density.
Claims31
A battery pack, comprising
- a) a first secondary cell connected to a second secondary cell;
- b) the first secondary cell having a first discharge capacity that substantially matches a second discharge capacity of the second secondary cell;
- c) the first secondary cell having a first internal resistance to a direct charge current that substantially matches that of a second internal resistance to the direct charge current of the second secondary cell;
- and
- d) wherein the internal resistance of the first and second secondary cells is calculable by measuring their charging voltage and charging current, then dividing the change in cell voltage by the charging current, and wherein the internal resistance and discharge capacity of the first and second secondary cells is calculated and determined before the first and second secondary cells are incorporated into the battery pack.
A method of forming a battery pack comprising the steps of:
- a) measuring a first discharge capacity of a first secondary cell;
- b) observing a first internal resistance to a direct charge current of the first secondary cell by determining a change in voltage and a change of current and dividing the voltage change by the current change;
- and
- c) connecting the first secondary cell to a second secondary cell having a second internal resistance to the direct charge current that substantially matches the first internal resistance of the first cell.
Dependencies are inferred from the claim text.