I've got an USB powered speakers but I'm not only using it with my laptop, I'm also using it with my MP3 player and my mobile phone.
Usually I'm using AC to USB 5V adapter to power up the speakers, but sometimes it's not practical.
Then I've got an idea to put battery on it, so it's become more portable.
To do that I'm only need to buy battery holder witch I can buy in any electronics supply store.
Then I open up the speakers, make a couple of holes and connect the cable from the battery to the power input on the circuit. Just as simple as that.
Now I have 3 options to power up my speakers:
1. USB from laptop.
2. AC power with adapter.
Sorry I don't have a step by step Instructables because it's very easy and I'm sure you all already know what to do.
Remember to put the battery on series first so we will get 6volts from it to power up the speakers.
Conversion on USB powered is a lot easier then the AC powered.