Much like Xbox One's controller, it is designed to accept AA's, because MS found that when surveying their fanbase, about half still like to use AA's. You can purchase a rechargeable battery pack for it, by buying the Xbox play and charge kit, but afaik it doesn't come bundled with one of those rechargeable batteries, just 2 non-rechargeable AA's.
Wow. I had no idea XB1 controllers still came with AA batteries. What's the price on a recharging kit new?