my psp won't charge!!!!!

my psp has been lost for about a year in a half, a couple of days ago my roomate found it for me. i just bought a new charger. so i opened it, then i checked the psp to see if it had any juice, it was powerless. so i plugged it in, and i began playing gta. it was working just fine. then i shut it off after playing for less than a few minuets, to see if it worked. i waited an hour with it hooked upto the charger, and i came back to check on it, i unplugged it, and turned it on, and there was nothing. it was as if i had never charged it at all!. the psp will only run when it's hooked up to a charger, but when i take it out, i can't get it to work. i'm thinking i need a new battery, not sure though.