Most likely the midplate is not contacting the main board properly. The midplate is the part of the part where the battery fits in. This part also houses parts like the camera and the speakers. The midplate connects to the mainboard electronically via a variety on contacts. If the contacts are not mating properly or are dirty, you have problems like you describe.
First, try gently tightening the six torx screws that hold the midplate on. The right middle screw has a white sticker on it. Remove it very carefully. If it's missing or broken, your warranty may be voided. Use an Exacto to bring up half of the sticker, then use tweezers to remove it.
If that does not work, remove the screws and take the midplate off. Gently clean the contacts and reassemble.