Charging problems

Hi guys , i would like to thank everybody that will be able to give me even a little advice to solve my problem ^^".... oh well lets start...

From a few weeks i'm having a problem with my charging sistem of my iPad2 (16gb , not upgreaded to iOS 6, but i think this is not the key of my problem), in particular all the times that i insert the cable on my device the battery begins charging , but after 5seconds it stops and restarts charge on its own periodically, with the resoult that in like 12h of charge it charges only for a 30% or less .... im particularly worried about my iPad battery .. so at the moment i turned off the device and planned to ask to a appleshop-assistant...any advice?....(sorry for my bad english but i think i've been at least understandable ^^"...) see ya.

P.s , i changed the charger and the cable 2 times , so the problem is not linked with it x_x"...