Coming from a Razr Maxx I know I'm gonna have to adjust to the smaller and highly complained about battery life of the GNEX.
Welcome to the club! If you register your device on Samsung.com you get a coupon for 50% off mobile accessories. You can get the extended battery and battery cover for $25 and if you order 2, you get free shipping. You might be able to find them cheaper on Amazon, though. The OEM batteries for the GNex have the NFC chip in them so if you are going to buy one of the non-OEM batteries, they might not have the NFC chip on them.
Also, GNex accessories are on clearance at Verizon online as well as in the stores. No batteries left online but you might find them in a store.
I have a charging cradle I got off of Amazon that I use so that I always have a fully charged battery on hand. If you are going to switch batteries frequently like I do, I recommend picking up extra battery covers because I broke mine from all the battery switching I do. The standard battery cover is $5 at VZW online and the extended battery comes with an extended battery cover.
Also, if you do battery switching, you have to constantly take your case on and off so keep that in mind when picking a case. I broke my Seidio case taking it on and off. Not all of the cases fit with the extended battery in, so keep that in mind, too.