Voltage supply to Arduino

As I mentioned in my last question, we are making a autonomous robot which uses gps and moves to the given location.We are using Arduino Mega omni wheels, gps module, ultra sonic sensors, dc motor encoders ,MPU9150.Can I supply 5v directly from a 18v(2 9v batteries in series) battery with L7805 voltage regulator in middle? I have read that it generates noise.Will that affect my bot performance? What's the better method?

Here is the link where it is advised to use two capacitors to reduce noise?


Are they really necessary or Will that work fine even without capacitors?

The capacitors are recommended on the [u]manufacturer's datasheet[/u]. Without them the regulator may oscillate, overheat, or otherwise not operate properly. (It's' going to get "warm" with 18V anyway, and if you can tap into the center of those batteries at 9V it will run cooler.)

Use batteries in parallel. what kind of batteries? can they provide sufficient current?
The 7805 very much like the caps (at least on output side)