There are extended battery packs sold in eBay but they make the Samsung Galaxy Nexus just plain ugly with a bulgy back bottom. That's the price to pay for extra hours to the smartphone. So instead of going ahead and order an extended battery pack and make your Samsung Galaxy Nexus fugly,
I scoured the Android Market to look for apps that can manage the smartphone power more efficiently to squeeze some battery life so i can use the smartphone till the sun comes down. Tried different apps and Easy Battery Saver is the best i found so far. This app manages the smartphone brightness and connectivity very efficiently.
Easy Battery Saver can take over the auto brightness control and able to dim the display further thus increasing a significant amount of battery life. I estimate about 10% to 15% of life out of my regular usage.
Easy Battery Saver can also takes control of the connectivity of mobile data and WIFI connection once the smartphone goes into sleep mode (display switched off) to save more battery power. How it does this is quite good where it will open all connectivity for a period of time (set in the application settings) and then shut down all connectivity down for another period of time (also set in the application settings). It cycles this actions during the sleep mode until i wake the smartphone up (switched display on). I found that this actually helps to increase the battery life so significantly until I could get around 50% charge left when i left my office at the end of the day.
Well the downside is if you are relying on real time push notifications from applications, this might not work for you. You might as well fork out some cash to order those 3800mAH battery pack that will make your Samsung Galaxy Nexus look fugly.
This is definitely a good app to pay for since it does it's job very good. It provides a few pre-configured settings for those who are not into setting up the application in detail and it also provide a custom settings mode for people like me who like to tinker around the settings for an optimize settings to suite my usage.