A Japanese Youtube user has posted a video displaying the battery life of the PlayStation Vita versus the 3DS. The PSP is there, too. But nobody cares about that.
The PSP used is a PSP-3000 with the expanded 2200mAh battery. The Vita's battery is a larger 2210mAh battery, but the beefier hardware taxes the battery at a faster rate. The 3DS battery is a 1300mAh battery. Let's see how they all stack up.
The PlayStation Vita runs out of life at the 3 hours and 47 minutes, while the 3DS gives in at 2 hours and 35 minutes. The PSP reigns supreme at 9 hours. But nobody cares about that.