Which Enegy source?

Hello :),

i finished my project and now i want do work the MSP430 G2553 standalone (without the Launchpad). It works with 3 ultra bright LEDs and are stored under the case of a lamp box with plexiglass.

What kind of batteries would you recommend me to hold those 3,3V for the longest time?

Or just tell me how you are driving your MSP430 standalone?

Thanks :)!