Similar to Xbox Live gamertags and PlayStation Network online IDs, BattleTags are the way that players name themselves within Blizzard’s Battle.net ecosystem. From Overwatch and Hearthstone, to World of Warcraft and Call of Duty: Warzone, although some of these titles may require/allow players to make separate in-game names, BattleTags are required for adding and playing with friends. Here's a breakdown of how to change your BattleTag name for free.
How to Change Your BattleTag Name for Free
Separate from the current promo, each Battle.net account is initially allowed one free BattleTag change. If you haven't yet used that free name change, log in to your Battle.net Account Details and select "Update" in the BattleTag section to do so.
If you do not have that free name change available, feel free to take advantage of Blizzard's current promotion. From now until Friday, Nov. 5, 2021, Battle.net users can request a free name change via Blizzard Support ticket form.
According to the site, it will take approximately 30 days or up to four weeks for Blizzard to process and add the free BattleTag Change to one's account, and that you will receive a notification once your request has been processed.
According to Blizzard, existing free name changes will not stack for future use, so in theory, if you were to use the initial free name change, and then try to use the current promotion, it might not fly.
It usually costs $10.00 USD for Battle.net users to change their BattleTag.
BattleTags do not need to be unique. You can use any name you want, as long as it follows Blizzard's Naming Policy. Each BattleTag is assigned a numeric ID to create a unique identifier (e.g. FallenSlayer#3592).