Off topic here, but were you aware the internal battery is rechargeable? It isn't charged from the main battery, but is charged by using the battery eliminator.
The "INTERNAL BATTERY" is not like a regular Lithium ION battery. It is a capacitor located on the main board inside the camera itself which keeps the settings, as well as power in the unit. The only way to have it "replaced" is by a service technician.
Is it safe to assume you are having setting issues?
Not easily changeable by the end user, as per above. You should be charging it every 3 months or so, by leaving the power button turned off and having it plugged into 110VAC with the power adapter for about 4 hours.