Can I use 3V (2\*AA or 2\*C batteries in series) as power for 10/20 leds connected in parallel?

**LED specs:**  

Diameter: 3mm / 0.1"  

Emitting color: Red/Green/Blue/White/Yellow  

Material: GaP  

Forward voltage: 1.8-3.4V  

Forward current: 20mA  

Backward voltage: 5V  

Wavelength: 460-630nm  

Frequency characteristic: Low frequency

I will connect only 1 collor lets say 20 red or 20 green leds... need them to work at 70-100% of intensity... the batteries model and number is not a limit I am just searching now...and yes I can make a connection of 3\*C batteries in series