Not Charging, Charging Erratically

Ok I have looked over the other posts but mine seems to be slightly different than the others. I have an iPhone 2G that I have changed the battery on, had no problems before the change save for the old battery draining very fast but also recharging very fast, after the first battery change it charged VERY erratically, it had 50% charge when I installed it, charged up to 88% quickly then it dropped to 66% instantly then up and down up and down etc for a day, after it got below 20% it refused to charge and died. I took that battery out and installed another brand new one and it seemed to be ok, it charged up to 100% the first time and discharged normally to 20% where I normally charge it, I left it overnight and woke up to a phone at 13% charged while plugged into the wall, hooked it up to the laptop and it refused to charge as well despite itunes recognizing the phone and the display saying it was charging, I unplugged the phone plugged it back in then all of a sudden it was at 38% charge from 11%, I kept this unplug replug procedure in till it said 66% where it stopped "charging" now it refuses to charge at all, itunes still sees it fine, I have tried 3 diff cables to no effect and now have a phone that displays the connected to power screen but wont take a charge anymore. Any ideas?