9v

Will i 9 volt battery power the ardunio mega 2560 without braking it?

A 9v battery will not damage the Arduino Mega, so long as you wire it through the internal voltage regulator: http://arduino.cc/en/Main/ArduinoBoardMega2560

The question is, why would you want to use a 9v battery? You're going to get horrendous run time with one of those. Better off using 6x AAs.

Sparkfun sells a 9V to barrel jack adapter.

Does the UNO use an LDO? I always assumed it did. If it doesn't then wizdum is right. You will get about 1/8 life out of the 9v before it is dead dead dead. I think drop out on a standard 5V regulator is something like 7V or close to that. I looked it up once when I was having this problem and didn't understand what I was doing wrong. Without an LDO and/or a boost regulator, you are sunk on a 9V and an LDO will only get you down to about 5.3V. Just not worth it.

Discussion here http://arduino.cc/forum/index.php/topic,87243.msg654510.html#msg654510

Go with 3 AAs (or Cs or Ds) into the 5V pin, bypass the regulator and reverse polarity protection diode.

ATmega2560/ATmega2561: • 0 - 16MHz @ 4.5V - 5.5V

so 3 AAs and were do i put it in???

mrdove500: so 3 AAs and were do i put it in???

Well ...

CrossRoads: Go with 3 AAs (or Cs or Ds) into the 5V pin

There isn't a jack or receptacle as such. There is the female pin header, where you could insert a lead.

so it is call AREF or IOREF or the vin one?

The 5V, it is the 5th hole down the left header behind the power connector.

Yes, just like I said:

Go with 3 AAs (or Cs or Ds) into the 5V pin.