Re manuals, sure, the FAA too in theory requires the latest manuals, but the "fact" is that most firms do not subscribe to the latest $1000/year ATP CD manuals for every type they work on. Many work off many years old microfilms. The GA maintenance scene would grind to a halt if this was actually enforced. It would also make a mockery of all owner maintenance provisions.
I suspect that anybody flying a G1000 plane won't worry about the cost of replacing the backup batteries
I have just my ELT battery to check each year. There is one in the KLN94 but that was never checked even when I was on PT G-reg. These batteries cannot be tested as such; they can only be lifed, or replaced when they are manifestly flat (config gets lots).
Radios... no issues, but I am hangared, keep 1kg of silica gel in the cockpit the whole time (and change it for freshly baked one every week, usually when I fly), and I think the old KX radios (I have a 155A and a 165A) were among the better stuff. I have had the usual KFC225 AP issues but little else - after the first 6 months or so when a lot of stuff packed up under warranty. Nothing corrosion related.