Water Damaged iPhone 4S Not Charging But Works

I have a water damaged iPhone 4S that works when I put a battery with charge in. However, when plugging into a power source; wall or PC, it does not charge, it shows the charging symbol, and iTunes can detect the phone, but the charge percentage doesn't rise, it only goes down. I have transplanted the board into a new chassis, to rule out dock connector, and used a known working battery, and it still doesn't charge. It has been a while since it was damaged, and I will try cleaning it today with some iso. If that fails, can anyone help me identify components of the charging circuit to be tested?

Thanks, Mike

EDIT:

I have also noticed that when the battery is disconnected, and plugged into a power source, the phone does not try to boot when trying to turn on. However when I try this with another 4S, it actually gets to the Apple logo before restarting.

So, maybe power is getting to the board, as it shows that it is charging, but the power is not getting to the battery, or the parts of the board that need it?