i have the charged simbol on the little battery in top right corner but when the big battery shows when telephone is lock it shows with bery liitle red line and no simbols underneath

My iphone 4 got wet yesterday (cortesy of my 2 year old).

It is working fine but when put to charge in the top righthand corner little icon comes as charged.

but when telephone is looked the big simbol in the middle shows as very low battery, when got my telephone reset by 3 it showed that have 4% battery but it has been going on like this for about 6 hours now and i have been using the telephone.

can anyone help please?