I'm asking you because a red that there are some risk to destroy the USB port if we use too much electricity from it...
maybe the tension is too low ?!
Quotemaybe the tension is too low ?!Yes it's too low. As described here it should be 7-12VDC.
I guess you need the battery so your project can be portable, mains free? Becasue if not, an easier solution is a say 9 or 12VDC wall adapter thingy with a 2.1mm centre-positive connector for the round socket.For long-term battery use, I'd solder a 2.1mm plug onto the battery leads instead of using the Vin and Gnd holes.
As soon as I get it, to connect it to the UNO, the (-) to the GND pin and the (+) to the Vin ?! Is it correct ?
Even if I connect the board to my computer in USB, the electricity used by the board will be the one from the battery ? Is it correct ?
Yes, i found a 12V DC Wall adapter with the correct connector. It's a 1A. I guess that this 1A suit good for the Arduino Uno