If you use three AA batteries, you will need resistors.  But if you use two AA batteries you will not.  Well I need to clarify that a bit. 

If you use blue, green or white LED's only then you will not need resistors with two AA batteries.  But if you use Yellow or Red LED"s then you will need resistors no matter what.  

One way around this is to paint white LED's the color you want with transparent paint.   I have done this before and it will work.

Two AA batteries will power 10 LED's for 40 to 50 hours, so no worries there.   I put 5 LED's in my viper three years ago, and they still light up the engines when I turn the switch.