I tried to make a "Betavoltaic" battery as my summer project but radioactive material costs too much 😡 The only way for a civilian/ebay user to get Tritium is by purchasing it in individual keychain cylinders of about 1 gram, and some tests I did showed that I would need a couple hundred dollars worth to generate any power.
The problem with an iPad powered by this is that a nuclear battery small enough to carry around with you would only generate a minute amount of electricity - barely even enough to power a wristwatch. The iPad would need a briefcase sized RTG weighing ~25 pounds to power it. (and it would also be *quite radioactive).
Just before the release of the last MBP I saw some people speculating that it might be powered by a fuel cell🙄