Yes, you read it right free Rock Band DLC when you purchase specially marked packages of Energizer Ultimate Batteries. Not a bad deal this time of year seeing almost everything we buy for Christmas needs batteries, and the DLC is available to both Xbox 360 Owners and PS3 owners alike.
Here is what HMXHenry a Harmonix developer had to say about the deal on the Rock Band forums:
I thought you RB.com forum regulars may be interested to know that the fine folks at Energizer have decided to give away DLC with their new Advanced Lithium Batteries.
This deal applies to both XBox Live and the Playstation Store, so if you’re in need of new batteries and some new DLC then this should work out nicely for everyone.