ipod touch 5th gen dies within 2 mins of not being pluged in

i got a ipod touch 5th gen for christmas and it worked great up until the last 2 months or so i will charge it all night and in the morning i will unplug it and check facebook and before i can even open the app it will die and wont turn on until i plug it in again. So whats the problom is it the battery or ios 7 and i didnt get water or anything on it so its not shorting out or anything like that. maybe theres somthing they changed in the 5th gen battery that doesnt work right. someone help!!