The arduinos in most of the tutorials have a 9V in, but mine does not. Mine has VIN, 2 grounds, 5V, 3V3, Reset. To power the arduino from a 9V battery, I have been going in to the 3V3 or the 5V, but I get the sense that this might not be good for the board. It does not work to go into the VIN. Soldering a 9V battery to a 2.5mm power plug has not worked either. Could this have something to do with the difference between the board in the tutorials and my board?
Did you move the PWR_SEL jumper from the two pins closest to the USB jack to the two pins closest to the power jack? That should let you use either the power jack or the VIN pin.
To power the arduino from a 9V battery, I have been going in to the 3V3 or the 5V, but I get the sense that this might not be good for the board.
Yes, Don't Do That (TM).
You're lucky if doing that didn't fry your ATmega168 chip.
You need to use the power select jumper and Vin as mentioned above.
--Phil.