Do you have a multimeter? [u]How to measure current[/u].
Somebody can probably tell you how much current the Arduino takes with nothing else connected, but I don’t know. If you are running motors or lots of LEDs, etc., of course your current consumption will go up.
A AAA alkaline battery is rated for about 1000 milliamp-hours and a AA battery is rated for about 2400 milliamp-hours so a AA will last about twice as long. According to the Energizer datasheet, mAh life is calculated by allowing the 1.5V battery to drain-down to 0.8V so unless you have more batteries for more “extra” voltage you won’t get full life from the batteries.
This can get a little tricky because 4 single-cell batteries is ~6V which is barely enough to power the Arduino through the voltage regulator. 6V (fresh batteries) is OK but of course you won’t get “full life” out of them.
If you add a couple more batteries for 9V you’ll get a lot more life because the Arduino will continue to operate until the batteries get down to around 5V. But, it’s not as “efficient” because the higher the voltage, the more energy you waste in the voltage regulator. (You won’t have to change batteries as often but in the long run you’ll spend more money on batteries.)
You can use 3 batteries and bypass the regulator, but then you’re starting-out at less than 5V and you’ll probably get even less battery life.
The ideal setup is to use a higher voltage with a separate switchmode voltage regulator. Switching regulators are nearly 100% efficient so you can actually get more current out than you draw from the battery (while reducing the voltage) and you can drain the battery down past it’s normal life.
Another question i have is i plugged a 9v battery to dc jack but the arduino wasn’t turned on so is it mean that the 9v battery isn’t enough power to turn the arduino on?
If you check the voltage, it’s probably no-longer 9V when you plug it in…