There's no need for an extended battery. You just need to be very smart about how you manage your battery life. For starters, turn off all location services to nearly double your battery life unless you absolutely need them.
I highly recommend you look into the developer section for information on how to root and install custom ROMs. The Galaxy Nexus is a developer's phone designed specifically for developers. It is very easy to heavily modify the software at great benefit to the end user, and the community is huge. Welcome and enjoy.