The backplate on this particular phone is held on with just some stubborn adhesive. With a heat gun, a spudger, and some patience you can have that back plate off in no time. Then it can be replaced with a new one and some fresh adhesive.
Lucky for you this particular phone is water repellent. However, that is not the same as water proof. If after the incident you feel like the water has made it inside the device then you should turn it off immediately, put it in a bag, and fill it with rice. The rice will soak up the moisture. Unfortunately you cannot pull off the back to remove the battery on this phone so turning it off will have to do.
If you have not already tried a different outlet and charger then I would recommend doing so first. If the issue still persists then you may have a bad battery, but you could also have a faulty charging port.