What is the battery voltage supposed to be (what is listed on it)? Is there a way to power the camera via a USB cable or some other external source? If it's a lithium battery and is at all low, it is not charged as lithium don't drop voltage as they are used the same way nicad batteries do. So if the battery is rated at say 7.6V, 7.4V would mean a battery not charged and you may see it drop under load. I have not tried to open up a DSLR\Mirrorless camera so I can't tell you much about the inside.