Possible to change iPhone battery for better battery life?

I'm going to get iPhone 4s and heard it's battery life runs out quickly. Could you buy a better one which lasts longer to replace?
Which are best and what is the price range?

Yes you can buy a new battery and replace it yourself it's easy!
Price range is probably $5-$20, buy a brand one!

I phones don't have removable battery. That's android phones. The phones battery life it's has now is what will last forever. I suggest getting a Samsung galaxy phone

IPhones do not have a removable battery, you'll have to use the one that comes with the phone. The battery life isn't really as bad as people make it out to be.