Andriasang, a Japanese YouTuber timed a freshly-charged PS Vita, a 3DS and a PSP 3000 from when they were booted up until they ran out of battery the reported results were as follows:
The 3DS ran out of battery at 2h 35m. running Monster Hunter Tri G
The PS Vita ran out of battery at 3h 47m. running Uncharted : Golden Abyss
The PSP 3000 ran out of battery at 9h. running Monster Hunter Portable 3rd
The 3DS ran out of battery at 2h 35m. running Monster Hunter Tri G
The PS Vita ran out of battery at 3h 47m. running Uncharted : Golden Abyss
The PSP 3000 ran out of battery at 9h. running Monster Hunter Portable 3rd