Synchronous playback with battery-powered playback device

1. A first playback device comprising:

a battery;

at least one communication interface configured to facilitate communication over at least one data network;

at least one audio amplifier;

at least one processor;

at least one non-transitory computer-readable medium; and

program instructions stored on the at least one non-transitory computer-readable medium that are executable by the at least one processor such that the first playback device is configured to:

while the first playback device receives a data stream and a battery level of the battery is above a threshold, forward at least some data from the data stream to a second playback device using the at least one communication interface;

while the at least some data from the data stream is being forwarded to the second playback device, detect that the battery level of the battery is below the threshold; and

after detecting that the battery level of the battery is below the threshold, (i) transmit at least one message comprising an indication that the first playback device will stop forwarding of the at least some data from the data stream and (ii) stop forwarding of the at least some data from the data stream to the second playback device.

2. The first playback device of claim 1 , wherein the data stream comprises an audio stream.

3. The first playback device of claim 2 , wherein the program instructions that are executable by the at least one processor such that the first playback device is configured to forward the at least some data from the data stream to the second playback device comprises program instructions that are executable by the at least one processor such that the first playback device is configured to:

forward audio content from the audio stream to the second playback device.

4. The first playback device of claim 3 , further comprising program instructions stored on the at least one non-transitory computer-readable medium that are executable by the at least one processor such that the first playback device is configured to:

using the at least one audio amplifier, play back the audio content from the audio stream in synchrony with the second playback device.

5. The first playback device of claim 3 , wherein the program instructions that are executable by the at least one processor such that the first playback device is configured to forward the audio content from the audio stream to the second playback device comprises program instructions that are executable by the at least one processor such that the first playback device is configured to:

forward the audio content from the audio stream to a plurality of other playback devices comprising the second playback device.

6. The first playback device of claim 5 , further comprising program instructions stored on the at least one non-transitory computer-readable medium that are executable by the at least one processor such that the first playback device is configured to:

using the at least one audio amplifier, play back the audio content from the audio stream in synchrony with the plurality of other playback devices.

7. The first playback device of claim 1 , wherein the program instructions that are executable by the at least one processor such that the first playback device is configured to forward the at least some data from the data stream to the second playback device comprises program instructions that are executable by the at least one processor such that the first playback device is configured to:

forward the at least some data from the data stream to a plurality of playback devices.

8. A method performed by a first playback device comprising a battery, the method comprising:

receiving, using at least one communication interface of the first playback device, a data stream;

while receiving the data stream and a battery level of the battery is above a threshold, forwarding at least some data from the data stream to a second playback device using the at least one communication interface;

while forwarding the at least some data from the data stream, detect that the battery level of the battery is below the threshold; and

after detecting that the battery level of the battery is below the threshold, (i) transmitting at least one message comprising an indication that the first playback device will cease to forward the at least some data from the data stream and (ii) ceasing to forward the at least some data from the data stream to the second playback device.

9. The method of claim 8 , wherein the data stream comprises an audio stream, and wherein forwarding the at least some data from the data stream to the second playback device comprises:

forwarding audio content from the audio stream to the second playback device.

10. The method of claim 9 , further comprising:

playing back the audio content from the audio stream in synchrony with the second playback device.

11. The method of claim 9 , wherein forwarding the audio content from the audio stream to the second playback device comprises:

forwarding the audio content from the audio stream to a plurality of other playback devices comprising the second playback device.

12. The method of claim 11 , further comprising:

playing back the audio content from the audio stream in synchrony with the plurality of other playback devices.

13. The method of claim 8 , wherein forwarding the at least some data from the data stream to the second playback device comprises:

forwarding the at least some data from the data stream to a plurality of playback devices.

14. A first playback device comprising:

a battery;

at least one communication interface configured to facilitate communication over at least one data network;

at least one audio amplifier;

at least one processor; and

at least one non-transitory computer-readable medium; and

program instructions stored on the at least one non-transitory computer-readable medium that are executable by the at least one processor such that the first playback device is configured to:

while the first playback device receives a first audio stream, transmit a second audio stream that comprises audio content from the first audio stream to a second playback device using the at least one communication interface;

play back, using the at least one audio amplifier, the audio content in synchrony with the second playback device; and

while the first playback device does not receive power from at least one external source;

detect that a battery level of the battery of the first playback device is below a threshold; and

after detecting that the battery level of the battery is below the threshold, (i) transmit at least one message comprising an indication that the first playback device will cease transmission of the second audio stream and (ii) cease transmission of the second audio stream to the second playback device.

15. The first playback device of claim 14 , wherein the program instructions that are executable by the at least one processor such that the first playback device is configured to transmit the second audio stream comprises program instructions that are executable by the at least one processor such that the first playback device is configured to:

while the first playback device receives power from the at least one external source, transmit the second audio stream to the second playback device using the at least one communication interface.

16. The first playback device of claim 14 , wherein the program instructions that are executable by the at least one processor such that the first playback device is configured to transmit the second audio stream comprises program instructions that are executable by the at least one processor such that the first playback device is configured to:

while the first playback device does not receive power from the at least one external source and the battery level is above the threshold, transmit the second audio stream to the second playback device using the at least one communication interface.

17. The first playback device of claim 14 , wherein the first audio stream is the same as the second audio stream.