According to 9to5Mac, the iPhone 5 battery won't differ a lot from the one the iPhone 4 had, which might disappoint Apple's fans. Battery is rumored to be with a capacity of 1440 mAh, while the iPhone 4S had a capacity of 130 mAh.
What's more, the fact that iPhone 5 will have a larger screen and LTE capability, means that battery life might be indeed shorter than what we were hoping. This can be guessed even without the rumors, as it happens with every new smartphone. Unfortunately, the fact that the smartphones are nowadays for various uses, makes them have their batteries draining every day, with the need of an extra battery increasing.
Until the market finds a way to increase significantly the battery life of the smartphone, we have to deal with the current battery and focus on all the other features that iPhone 5 will have. There are so many advantages anyway that we don't have to be disappointed yet. At least, not without actually using it. Wait until September 12 then!