how much more battery life does the 14 inch have?

Both claim up to 6 hours according to Apple's iBook site.

 

I've heard the same thing a few times but I really doubt it's true, and if it is, I don't think the differences would be all that major.

 

I've actually gotten close to seven with mine before- but that was with all the settings turned down.

 

Yes, the 14" iBook has a larger battery. However, it also has a faster processor and a larger screen to light, so it uses more power than a 12". So it's a crapshoot.