Im wanting to power my arduino via a battery pack. what kind of jack should be used, and is there any where on the arduino boards, uno and mega, that i can solder the wires to instead?
barrel jack 2.1mm inner 5.5 outer.
Power can be supplied to Vin-pin and gnd
If your supply is 5V (4V..5,5V) regulated - go to 5V-rail (bypassing onboard regulator)
Jaychad:
Im wanting to power my arduino via a battery pack. what kind of jack should be used, and is there any where on the arduino boards, uno and mega, that i can solder the wires to instead?
You can solder wires to the bottom of the board under the power input jack. There's some big solder joints there, perfect for adding a wire.
There's three pads. Check with a multimeter to see which pin is which. Two are connected to GND, one is connected the center pin of the jack.
awesome. Thank you again
Mate, pop into Maplin, order code HH60Q. 
on my way 