Get an AMP and Voltage usb device to check what current you are getting as charging for your phones.|
If you get less than 0.80 AMP or less than 1 AMP the charging will be very slow and depends on the size of your battery.
Possible fix : Change the charging board of your device if you are getting a slow charge , but the battery lasts. (You can try to sottor the components back again, but that might not be the only thing malfuncioning in the charging board)
Possible fix : If you are not getting any Voltage or AMP's from the charger than you may need to change the battery as well.