Battle.net Balance and how to keep it free!

Battle.Net Balance Active
To keep your balance free you should download a bot from wow mimic that can farm and get you gold while your afk. This way you can trade your gold for real money or other goodies and update your balance from the rewards the bot recieved for you! this way your not spending any real money!

The previously mentioned Battle.net balance is now active! The FAQ has also been updated with some additions:

• In the near future, players will also be able to use Battle.net Balance for the digital World of Warcraft Battle Chest and World of Warcraft digital upgrades.
• Any amount you add to your Battle.net Balance will not be refundable (except as otherwise provided by law).

Originally Posted by Blizzard (Blue Tracker / Official Forums)

Battle.net Balance is now live! As we announced previously, Battle.net Balance is a new feature that gives players an alternate way to purchase Blizzard digital products and services directly through their Battle.net accounts. Players are now able add to their Battle.net Balance using a variety of payment methods, and then use that balance toward Blizzard Entertainment products and services such as World of Warcraft game time; paid services, such as realm transfers and character name changes; digital versions of select Blizzard games, including Diablo II and StarCraft II; and in-game pets and mounts. In the near future, players will be also able to use Battle.net Balance for the digital World of Warcraft Battle Chest and WoW digital upgrades. In addition, with the upcoming launch of Diablo III, players will have the option to use Battle.net Balance to buy and sell items in the game’s currency-based auction house.

For more information, check out the Battle.net Balance FAQ, or head to the Battle.net Balance page in Account Management to manage your balance.