If your battery only lasts four hours when the iPad is plugged into the charger the you could have a defective charger, cord, or iPad itself. Try using a different outlet and also try charging a different device. If a different device charges normally then the iPad is faulty. If a different charger and/or cord works to charge your iPad then the charger, cord or both are defective. If you have a nearby Apple Sore, take the iPad, Harper and cord to the Genius Bar for a free diagnostic as soon as the store reopens.
If your iPad is less than 90 days old you should have free telephone technical support. Call them before trying the Apple Store and describe the problem. It’s possible that they will simply replace your iPad under warranty if they believe it’s defective.