System and method for managing parallel-connected battery cells

1. A system for managing a rechargeable battery comprising two or more battery cells or series stacks of cells, comprising:

a set of switches adapted for connection to a battery comprising two or more battery cells or series stacks of cells, each of said switches arranged to connect a respective one of said battery cells or stacks of cells between positive and negative nodes when actuated, or to connect one cell in a series stack of cells to another of said cells in said series stack of cells when actuated, said system arranged such that when all of the switches in a given series stack are actuated, said series stack is connected between said positive and negative nodes;

an electrical load directly connected to said positive and negative nodes; and

a controller arranged to:

determine the state of each of said battery cells or series stacks of cells based on one or more predetermined characteristics of each cell or series stack of cells; and

selectively actuate said switches based on the states of said battery cells or series stacks of cells so as to enhance the life of said battery.

2. The system of claim 1 , wherein said predetermined characteristics include one or more of the following: open circuit voltage across cell or series stack of cells, voltage across cell or series stack of cells under load, current provided by cell or series stack of cells under load, internal resistance of cell or series stack of cells, temperature of cell or series stack of cells, ambient temperature, rate of aging of cell or series stack of cells, cell or series stack of cells charge capacity, cell or series stack of cells state-of-charge (SOC), and/or number of charge cycles undergone by cell or series stack of cells.

3. The system of claim 1 , wherein said controller is further arranged to attribute a strength value to each of said battery cells or series stacks of cells based on its state.

4. The system of claim 3 , wherein each of said battery cells or series stacks of cells is subject to complete or fractional charge/discharge cycles, said controller arranged to actuate said switches such that cells or series stacks of cells having higher strength values are subjected to more complete or fractional charge/discharge cycles than are cells or series stacks of cells having lower strength values.

5. The system of claim 3 , wherein said controller is arranged such that cells or series stacks of cells having a strength value that is below a predetermined threshold are connected between said positive and negative nodes only when cells or series stacks of cells having a strength value that is above said predetermined threshold are at least partially discharged.

6. The system of claim 3 , wherein said electrical load conducts a current from said battery, said controller arranged such that cells or series stacks of cells having a strength value that is below a predetermined threshold are connected between said positive and negative nodes only when said load current is above a predetermined threshold.

7. The system of claim 1 , further comprising an algorithm that is executed by said controller in order to determine which of said switches to selectively actuate.

8. The system of claim 1 , further comprising a battery charging circuit arranged to be coupled to said positive and negative nodes, said controller arranged to actuate said switches such that said cells or series stacks of cells are selectively connected to said battery charging circuit.

9. The system of claim 8 , wherein said controller is further arranged to attribute a strength value to each of said battery cells or series stacks of cells based on its state, said controller arranged to actuate said switches such that cells or series stacks of cells having higher strength values are subjected to a higher final charging voltage than are cells or series stacks of cells having lower strength values.

10. The system of claim 1 , wherein said controller contains circuitry needed to determine the state of each of said battery cells or series stack of cells.

11. The system of claim 10 , wherein said controller is arranged to measure and/or calculate one or more of said predetermined characteristics of each cell or series stack of cells.

12. The system of claim 1 , further comprising a rechargeable battery comprising two or more battery cells or series stacks of cells to which said system is coupled.

13. A method of managing a rechargeable battery comprising two or more battery cells or series stacks of cells, comprising:

for a battery which comprises two or more battery cells or series stacks of cells, determining the state of each of the battery cells or series stacks of cells by measuring and/or calculating one or more predetermined characteristics for each cell or series stacks of cells;

based on the states of said cells or series stacks of cells and to enhance the life of said battery, actuating a set of switches to selectively connect said battery cells or series stacks of cells between positive and negative nodes and/or to connect one cell in a series stack of cells to another of said cells in said series stack of cells, said switches arranged such that when all of the switches in a given series stack are actuated, said series stack is connected between said positive and negative nodes; and

directly connecting an electrical load between said positive and negative nodes.

14. The method of claim 13 , wherein said step of determining the state of each of the battery cells or series stacks of cells comprises determining one or more of the following: open circuit voltage across cell or series stack of cells, voltage across cell or series stack of cells under load, current provided by cell or series stack of cells under load, internal resistance of cell or series stack of cells, temperature of cell or series stack of cells, ambient temperature, rate of aging of cell or series stack of cells, cell or series stack of cells charge capacity, cell or series stack of cells state-of-charge (SOC), number of charge cycles undergone by cell or series stack of cells.

15. The method of claim 13 , further comprising attributing a strength value to each of said battery cells or series stacks of cells based on its state.

16. The method of claim 15 , wherein each of said battery cells or series stacks of cells is subject to complete or fractional charge/discharge cycles, said step of actuating said switches to selectively connect said battery cells or series stacks of cells between said positive and negative nodes performed such that cells or series stacks of cells having higher strength values are subjected to more complete or fractional charge/discharge cycles than are cells or series stacks of cells having lower strength values.

17. The method of claim 13 , further comprising coupling a charging current to said positive and negative nodes and actuating said switches so as to selectively connect said battery cells or series stacks of cells between said positive and negative nodes such that said battery cells or series stacks of cells are selectively charged by said charging current.