I've been wanting to do this for a long time. Portable speakers are often very expensive and not loud enough. I got my hand on some old speakers and I would like to turn them into a portable speakers. What are the main steps I should do to achieve this? Could this be done by only removing the 230V -> 9V converter and simply connecting a battery to the place where I cutted the wires. Could you give me an approximate time of how long would a 9V Alkaline battery last on a 18W speaker considering that it would be on 80% power most of the time? Thanks.