The link was to a DL article, but really all they did was link to the product on VZW's website. It seems like the trick to getting the discount is that you have to sing out of your VZW account, completely close your browser, re-open, go back to VZW, choose shop, browse ti the G-Nex Extended battery, specify that your device is the G-Nex (at this point it should be showing that it is $49.99) add it to your cart and say you want to check out now and on the next page it should show it as $24.99. After that you just manually enter in your address and CC and everything boom, a 50% off extended battery.
You may be able to do it without all the sign-out crap, but a lot of people were having their corp. discount show up which overrides the 50% off... some others were having a 25% off show up until they signed out. Some people also claimed they got it to work in-store. I called 611 to see if she could override my corp. discount before I figured out you had to sign out and she said that nothing in her system said anything about it at all and it must be a glitch.
Edit: Original Article:
[Deal] Galaxy Nexus Extended Battery is Half Off at VerizonWireless.com, Just $25 – Droid Life