i have problem with charging my Iphone 4S

i have problem with charging my Iphone 4S

often when i charge it , the operation of charging is not started although i see the sign of charging appear on the screen but the percentage of charge didn't make any progress , when i left it more time in charging case the precentage of charge battery go down till the mobile go down

with my tries randomly cases or little cases the charge start and work normaly