How many shots are taken, or is this a few days when turned off/on standby?
Is the WiFi activated? There has been some internet chatter that even if the camera is in standby mode, and the wifi button is pressed by something in the bag it may try to connect to a non-existent network. Try deactivating the WiFi option completely if you can.
Also, sometimes batteries take a few chargings to get up to full efficiency. Even in storage batteries can run down (thought they are getting better) so if the battery has been on the shelf in the store for a while it just needs to be conditioned by a few recharge cycles.