Iphone 4 Very strange charging problem?

Hi all,

My friends iphone got water damaged quite badly so i suggested id have a go at fixing it for him.

anyway took the phone apart cleaned it all with methylated spirit put it all back together and nothing...

So i tried the battery out of another iphone 4 which i knew worked fine as it was working in the other phone still nothing.

Put the old battery back in and left it on charge for 2 days , tried connecting to pc multiple times , still nothing...

I left the phone on its own not connected to anything for around 3 week was just about to give it him back but i decided to plug it in one more time and sucess!!

The low battery logo appared and the iphone charged as normal!

anyway i let the phone get upto 15% then i unplugged it so i could put a sim in , everything went to plan.

plugged it back into the charger and the phone will not charge anymore!!

its very very strange

I tried plugging it into the pc and it did nothing but i know it is receiving the connection from the cable because if i turn off the iphone plug it in it turns its self back on but it just doesnt charge ive disconnected and reconnected many times and had no joy.

my only guess is that the pins in the charging point some are working as should and others not so im guessing thats my next plan of action to fit a new charging point.

Would anybody suggest anything else ? ive turned off the phone as i dont want it to run out of battery and be completely dead again.

Thanks!