it isn't regulated... so it is what ever voltage your battery is at. 3s could be as high as 4.2*3 (or higher if you over charge) -> 12.6 or as low as 3.4*3 = 10.2 (or lower depending on how low you discharge your batteries)
@Squashymoon125 - you can buy a multi-meter (voltmeter) at Harbor Freight for around $5. Comes with a book too. I got mine for free with a coupon. This is a good way to start learning about electronics. It also lets you "see" all those little electrons.