250
A tiny radioactive battery could keep your future phone running for 50 years
(www.techradar.com)
This is a most excellent place for technology news and articles.
Most current phones use lithium ion batteries that can combust or explode in your pocket if tampered or damaged, but you don't seem to be worried about that. You only seem to be worried about the battery in the article because the only thing you remember about radiation from your high school physics is "radiation bad". Had you paid more attention in school you wouldn't need my smug ass correcting you.