A few weeks ago I popped the case on my 240 Series 2 DVR that I have had since September 2003. I did that to blow out the accumulated dust and was sort of surprised to found very little. I don't remember seeing anything about this in the forums and I have been checking them for over a year.
My other 240 Series 2 DRV is a few months newer and I didn't open that one because the other one was so clean. I assume that it is much like the older one.
What I did find was that there is a disk battery on the board like on computer motherboards that keep the BIOS working when the computer is off. I suppose that is the same function on the DVR like the computer.
I am wondering what happens when that battery depletes. I think it is a lithium. These are fairly long lived--maybe up to ten years if not used much. I don't suppose it is used very much since these DVRs stay running 24-7-365 except for an occasional unplug to move it or something like open the case (it's on an UPS).
What are the symptoms of a low or dead motherboard battery? Should I change it soon or wait for symptoms? It is like doing it on a computer? (Redo the BIOS)