You need to determine if the battery is being charged and capable of holding a charge.
Use a battery utility, such as coconutBattery (for Mac) or 3uTools (for Windows). It will tell you what the health of the battery is. Anything less than 80% of design capacity will require replacement.
If you have access to a USB Ammeter, you could use that to determine if the phone is really drawing current when it says it's charging.
If you have access to a multimeter, measure the voltage of the battery. A fully charged battery should read 4.2V.
It is also possible that the problem is with the charge circuit on the logic board but first we need to determine if the battery is at fault. Get back to us with your findings so we can give yo more guidance.