I have a problem with my Nikon D7100: it does not keep the chosen settings over time. For example, if I set the settings to take a picture at ISO 500 and after a series of shots it goes to ISO 1000. Or I set it to take the shot only in jpg and it reconfigures to take the shot in RAW.
The same thing happens to me with the menu settings; for example, if I set the internal brightness of the camera to +3, turn the camera off, turn it back on and it is +4 as it came from the factory.
What could be causing this - is it possible that it is a problem of some internal battery?