Apparatus, systems, and methods for charging partial use batteries

1. A computer-implemented method comprising:

determining a transition duration for a partial-use battery of a power supply, wherein:

the power supply will make a transition from a first power source to a second power source;

the partial-use battery supplies power to the power supply during the transition; and

the transition is expected to last for the transitional duration;

estimating an age of the partial-use battery;

calculating, based at least in part on the age of the partial-use battery, a partial charge voltage for the partial-use battery that will enable a discharge cycle of the partial-use battery to last for the transition duration; and

floating the voltage of the partial-use battery at the partial charge voltage to prolong the life of the partial-use battery.

2. The computer-implemented method of claim 1 , wherein

the partial-use battery comprises a backup lithium-ion battery.

3. The computer-implemented method of claim 1 , wherein:

the first power source comprises mains power;

the second power source comprises one or more alternating-current generators; and

the transitional duration is equal to a sum of a start-up duration of the one or more alternating-current generators and a buffer duration.

4. The computer-implemented method of claim 1 , wherein:

the first power source comprises one or more alternating-current generators; and

the second power source comprises mains power.

5. The computer-implemented method of claim 1 , wherein the power supply supplies power within a data-center rack.

6. The computer-implemented method of claim 1 , wherein the partial charge voltage is calculated to enable the discharge cycle of the partial-use battery to last for a sum of the transitional duration and a buffer duration.

7. The computer-implemented method of claim 1 , wherein:

the partial charge voltage is less than a voltage limit of the partial-use battery; and

the voltage limit of the partial-use battery comprises one of:

a voltage of the partial-use battery when the partial-use battery is considered fully charged; or

a nominal voltage of the partial-use battery.

8. The computer-implemented method of claim 1 , wherein estimating the age of the partial-use battery comprises using a nominal capacity of the partial-use battery to estimate the age of the partial-use battery.

9. The computer-implemented method of claim 1 , wherein:

estimating the age of the partial-use battery comprises using a measured capacity of the partial-use battery to estimate the age of the partial-use battery; and

the measured capacity of the partial-use battery was measured when the partial-use battery was manufactured.

10. The computer-implemented method of claim 1 , wherein estimating the age of the partial-use battery comprises:

measuring a present capacity of the partial-use battery; and

using the present capacity of the partial-use battery to estimate the age of the partial-use battery.

11. The computer-implemented method of claim 1 , further comprising:

estimating, at a subsequent point in time, an updated age of the partial-use battery;

calculating, based at least in part on the updated age of the partial-use battery, an updated partial charge voltage for the partial-use battery that will enable a subsequent discharge cycle of the partial-use battery to last for the transition duration, wherein the updated partial charge voltage is greater than the partial charge voltage; and

floating the voltage of the partial-use battery at the updated partial charge voltage to further prolong the life of the partial-use battery.

12. The computer-implemented method of claim 1 , wherein the transition duration is less than or equal to 90 seconds.

13. A backup-battery charging system comprising:

a power supply that will experience a transition from a first power source to a second power source, wherein the transition is expected to last for a transitional duration; and

a battery backup unit that comprises:

a backup battery that supplies power to the power supply during the transition;

a determining module, stored in memory, that determines a backup discharge duration for the backup battery, wherein the backup discharge duration is greater than or equal to the transitional duration;

an estimating module, stored in memory, that estimates an age of the backup battery;

a calculating module, stored in memory, that calculates, based at least in part on the age of the backup battery, a partial charge voltage for the backup battery that will enable a discharge cycle of the backup battery to last for the backup discharge duration;

a charging module, stored in memory, that floats the voltage of the backup battery at the partial charge voltage to prolong the life of the backup battery; and

at least one processor that executes the determining module, the estimating module, the calculating module, and the charging module.

14. The backup-battery charging system of claim 13 , wherein the estimating module estimates the age of the backup battery based at least in part on at least one of:

a nominal capacity of the backup battery; or

a measured capacity of the backup battery that was measured when the backup battery was manufactured.

15. The backup-battery charging system of claim 13 , wherein the estimating module estimates the age of the backup battery by:

measuring a present capacity of the backup battery; and

using the present capacity of the backup battery to estimate the age of the backup battery.

16. The backup-battery charging system of claim 13 , wherein:

the battery backup unit further comprises a register that is accessible to the power supply;

the charging module floats the voltage of the backup battery at the partial charge voltage by:

writing a value indicating the partial charge voltage to the register; and

issuing a command to the power supply to charge the backup battery; and

the power supply charges the backup battery in response to the command by:

reading the value indicating the partial charge voltage from the register; and

charging the backup battery to the partial charge voltage.

17. The backup-battery charging system of claim 13 , wherein:

the first power source comprises mains power;

the second power source comprises one or more alternating-current generators; and

a start-up duration of the one more alternating-current generators is less than or equal to the transitional duration.

18. The backup-battery charging system of claim 13 , wherein:

the power supply supplies power within a data-center rack;

the backup battery comprises a lithium-ion battery; and

the backup discharge duration is less than or equal to 90 seconds.

19. A battery backup apparatus comprising:

a backup battery that supplies power to a power supply during a transition of the power supply from a first power source to a second power source, wherein the transition is expected to last for a transitional duration; and

a battery-management subsystem that:

determines a backup discharge duration for the backup battery, wherein the backup discharge duration is greater than or equal to the transitional duration;

estimates an age of the backup battery;

calculates, based at least in part on the age of the backup battery, a partial charge voltage for the backup battery that will enable a discharge cycle of the backup battery to last for the backup discharge duration; and

floats the voltage of the backup battery at the partial charge voltage to prolong the life of the backup battery.

20. The battery backup apparatus of claim 19 , further comprising a register that is accessible to the power supply, wherein:

the battery-management subsystem floats the voltage of the backup battery at the partial charge voltage by:

writing a value indicating the partial charge voltage to the register; and

issuing a command to the power supply to charge the backup battery; and

the power supply charges the backup battery in response to the command by:

reading the value indicating the partial charge voltage from the register; and

charging the backup battery to the partial charge voltage.