Power Feeding Problem

The battery is above 7V. But when connecting to arduino The voltage at the at the port is lessthan 5V.
Whats wrong with it? I cant do an important project. Plz help!!!!

Which port are you talking about?

If it’s the jack, the following might apply.

Any power source has an (internal) output resistance. At the moment that you start drawing current, ohm’s law states that there will be a voltage (drop) over that resistance. When measuring the battery voltage with a volt meter, you’re only drawing a small current due to the high input resistance of the meter and the drop over the output resistance of the battery is small. The Arduino draws a lot more current than your voltmeter, so the voltage drop is higher and you will be measuring a lower voltage over the battery.

Are you using a 7V battery or a 9V or … ?

If it’s not a 7V battery, your battery is ‘empty’. If it’s a 7V battery and it used to work before with that battery, it’s empty as well.

If it's an output port, how much is 'less than 5V'. And what is connected to it?