"Zero, give or take measurement errors." As related to the GP's assumption "seems a bit harsh to the cat" - in other words, "why are you microwaving your cat, you monster!!111!", not as related to data transfer.
Edited to add the direct quote.
Edited to add the direct quote.
The answer is "no, your cat won't get its brains cooked, not even after prolonged exposure" - there's not even enough juice in the battery to do that :)