Why won't my iPad turn on?

You have to determine if this is a battery/charging issue or something else. Try these steps to help isolate the issue (in order):

1. Always try another Lightning cable and charger, preferably Apple original or MFi certified units. Does an iTunes enabled computer recognize the device?
2. The Lightning cable 8-pin connector should be sitting flush with the housing and completely inserted. If it is not, there could be lint/dust/debris inside the port impeding a proper connection. You can clean it out with a toothpick, fine point tweezers or a dental pick. Just be careful not to damage the pins inside the Lightning Port.
3. You can use a USB Ammeter to determine if the device is really drawing current when it says it's charging. If it isn't drawing current, then it could be a bad charge port or battery.

At this point, you need to get back to us with more info on your troubleshooting. You may also need to start replacing stuff, which means opening your device. Check out this guide to see if you are comfortable with the work required.