Originally Posted by Mirari
Raymarine when it comes to Autopilots are the worst.
It is indeed interesting how different folks have different experiences.
I have an ST6002 and have sailed many 1000's of miles with it including ocean passages, I use it just about every time I go sailing and I have never had a single moment of trouble with it. In fact I believe it to be the most reliable piece of kit on my boat.
As it happens I have two friends that have done several ocean crossings each, also have ST6002s also use them almost every time they go sailing and we often discuss how good these things are.
Are you sure there isn't something else on your boat that is possibly going to cause a problem with whatever AP you install?
To answer the OP, I don't know whether there is an internal battery or not on the AP but I know that many times I have completely removed all form of electrical power from my boat (physically removed all batteries) for assorted reasons and I have only once had to re-programme the AP and that was when there was a problem with the location of the fluxgate when I originally bought the boat, caused by the previous owner/installer.
I had a serious charging problem once, got a huge voltage surge that blew other instruments out and the AP survived with no problem. And when the batteries are getting to the absolute end of their capacity, the last electrical device that stops working is the AP and even then it gives a warning that it is going to shut down.