ipod 5g trouble charging

i purchased a previously used ipod 5g and have had it for around 3-5 months. i do not know how long the previously owner owned it for. it has worked great overall throughout the time i have owned it but lately it has had a problem charging. it charges at the same speed all though i have noticed that the charge doesent last as long. the main problem is that it is hard to charge the ipod. i have to put the wire at a certain angle and the slightest movement cuases it to stop the charge. once i find the angle and settle it charges good. i just want to know if this means the device has a problem and if so how could i fix it and what is it and or if its the chargers problem