System and method for powering a device

1. A system for powering a device comprising:

at least one internal battery located in a device;

at least one external battery connected to the device; and

a master controller configured to connect either the at least one internal battery or the at least one external battery to a power bus to power the device,

wherein the master controller is configured to:

determine the capacity of the at least one internal battery, and when the capacity of the at least one internal battery is below a threshold; and

determine whether to charge the internal battery using an AC adapter or from the at least one external battery.

2. The system of claim 1 further comprising a battery charger for charging the at least one external battery.

3. The system of claim 1 wherein the at least one external battery includes built-in circuits for measuring state-of-charge.

4. The system of claim 1 further comprising a holster configured to accept and secure the at least one external battery.

5. The system of claim 1 wherein the at least one external battery powers the device.

6. The system of claim 1 further comprising at least one AC adapter.

7. The system of claim 1 wherein the master controller configured to recharge the internal battery using the at least one external battery.

8. The system of claim 1 further comprising wherein the master controller is configured to:

determine when to switch from receiving power from the internal battery to receiving power from the at least one external battery.

9. A system for powering a device comprising:

at least one internal battery located in a device;

at least one external battery connected to the device; and

a master controller configured to connect either the at least one internal battery or the at least one external battery to a power bus to power the device,

wherein the master controller is configured to:

determine the capacity of the internal battery; and

when the capacity of the internal battery is below a threshold, determine whether to charge the internal battery using an AC adapter or from the at least one external battery.

10. The system of claim 9 further comprising wherein the master controller is configured to:

determine the external battery has been disconnected from a holster; and

switch to use the internal battery to power the bus.

11. The system of claim 9 further comprising wherein the master controller is configured to:

determine if an external battery is connected to the system;

if an external battery is connected to the system, connect the external battery to the power bus; and

disconnect the internal battery from the power bus.

12. The system of claim 9 further comprising wherein the master controller is configured to:

determine the external battery remaining capacity is below a predetermined threshold; and

command the internal battery to switch to power the bus.

13. The system of claim 9 further comprising wherein the master controller is configured to:

power the device using a first external battery;

disconnect the first external battery from the device;

connect an internal battery to a power bus to power the device;

connecting an AC adapter to the device;

charging the internal battery using the AC adapter;

disconnect the AC adapter from the device;

connect the first external battery to the device; and

charge the internal battery using the first external battery.

14. The system of claim 9 further comprising wherein the master controller is configured to:

power the device using a first external battery;

disconnect the first external battery from the device;

connect an internal battery to a power bus to power the device;

connect an AC adapter to the device; and

charge the internal battery using the AC adapter.

15. The system of claim 9 further comprising wherein the master controller is configured to:

power the device using a first external battery;

disconnect the first external battery from the device;

connect an internal battery to a power bus to power the device;

connect a second external battery to the device;

disconnect the internal battery from the power bus; and

connect the second external battery to the power bus.

16. The system of claim 9 further comprising wherein the master controller is configured to:

monitor the capacity of an internal battery;

determine the capacity of an external battery;

determine whether the internal battery capacity is less than a predetermined threshold; and

if the internal battery capacity is less than a predetermined threshold, and the external battery capacity if above a predetermined threshold, charging the internal battery using the external battery.

17. The system of claim 9 further comprising wherein the master controller is configured to:

determine if an external battery is connected to the device;

if not, the master controller allowing the internal battery to power the bus;

if an external battery is connected to the device;

determine the capacity of the external battery;

if the capacity exceeds a predetermined threshold, disconnecting the internal battery from powering the bus; and

connect the external battery to power the bus.

18. The system of claim 9 further comprising wherein the master controller is configured to:

determine if an external battery is connected to the device;

if not, the master controller allowing the internal battery to power the bus;

if an external battery is connected to the device;

disconnect the internal battery from powering the bus; and

connect the external battery to power the bus.