This is what I've now. I can attach a 9V battery. My friend drilled two small holes for the cables and solder them for me.
The input now can be also used an always on port if needed.
http://www.philohome.com/pf/pf.htm has some information that might help -- or here http://www.instructables.com/id/make-a-tiny-battery-for-LEGO-power-functions/?ALLSTEPS
Instead of the power functions battery, I would like to use a 9V battery.
I want to solder cables, but I don't know which one to do. Can someone give me details?
