Finished!

Step 6: Finished!

Take pride in knowing you put an old unloved speaker to good use, and enjoy the high quality audio now at your disposal anywhere, anytime.

Improvements:

A low battery indicator. I thought of this after I was nearly finished but a transistor and voltage divider could activate an LED when the battery drops below a particular voltage. Could definitely come in handy and would also help prevent over-draining the battery.
A different battery technology. A lighter or more powerful battery technology would increase the battery life and weight quite a bit. They are, of course, more costly and require special charging circuit otherwise they pose a major fire hazard.
Bigger more powerful amplifier. The TDA2003 design is scalable, so a more powerful amp circuit could be devised, but the battery life will take a hit unless upgraded as well. If someone wanted to build a large cabinet with a full car battery inside then a 100W amp may be required. High power amplifiers for car audio can be purchased as kits for relatively cheap on the internet.

Please feel free to ask any questions or post suggestions. Thanks for reading!