Kripton wrote in message ...
On 2012-01-19 12:31:10 +0100, "William Sommerwerck"
said:

Buy an inverter that converts 12V DC to 120V AC. Then use an
AC power supply ("wall wart") suitable for the boombox. It might
even have its own built-in AC adapter.

total waste of energy ...

WHY?
It requires no energy -- it's plug 'n play.

I'm not talking of human energy, but electricity energy ...
each time you convert voltage (12v-120V) then 120V-9V
you have power losses, that generate heat.
that means the energy if transformed into heat, useless and poor solution
for the planet ...
instead use a smps converter from 12vdc to 9vdc they exists
they are cheap, and the power losses are reducted to a minimum

I don't blame you for wanting to be green, but the energy involved is tiny,
compared to the energy the engine uses. For example, 20HP is about 15kW. Ten
watts (at worst) to run a boom box is nothing.