I just noticed this thread, sorry for late information.
I have had to recap 3 A820MCHs. It isn't fun, but worth the work when you start noticing poor bass response, auto alignment glitches, and... shorting caps. If you haven't already, I would upgrade the machine to the latest software. A lot of useful features are on it, and the machine as a whole, will work better. To see if you have the latest software, reference this list.
http://recordist.com/studer/SW_Reference_Liste.pdf
When you replace those batteries (only on MPU boards), you should to erase the memory by removing and shorting IC 8 (ram) pins to a sheet of metal. By doing that, all the parameters, presets, and soft keys will reset to defaults, so you will have to re-calibrate all the tensions, audio, etc.
As far as the caps go, you only need to worry about the electrolytics like others have said. Replacing all of those, and servicing the machine will take you the better part of 2 weeks to do. No joke. Anyone doing it faster is missing a step or on meth. There are more caps in there than some recording consoles.
Here is an updated audio cap parts list I made for a recent job.
http://greg.electrical.com/otherphotos/studer%20recap/Studer%20recap%20parts%20list.pdf
These are fantastic machines. That is all we track to at our studio. I encourage tech-heads to download the manual to look at design for fun. The schematic of the "line amp tranfoless" is interesting enough on it's own. Total overkill.
