before i did that i noticed that the 9 volt rechargeable battery that i was using did not give off 9 volts.
on the battery itself it said below 9 volt part in small text "7.2V-150" mAh.
can someone tell me how much power the arduino uno needs?
After having to go through the series polarity protection diode, 7.2vdc is just at the threshold of the auto-voltage selection function for the board. I would suggest that one needs at least 7.5vdc at the external power connector to reliably trigger the board's auto-voltage selector switch.
So you need a higher voltage if you want to utilize external voltage connector to power your board, 7.2vdc doesn't cut it. And a small 9vdc barrey (even if providing 9 volts) is still a poor choice to power an arduino board because of the low current capacity they offer.