From exploding phones to dangerous hoverboards: Why are batteries catching fire so often?

Just two weeks after the launch of the Galaxy Note 7 phone, Samsung was forced to recall 2.5 million devices worldwide, after reports that many were overheating, or even exploding Do YOU count on your fingers? Experts say it could actually... The 760mph train that'll take you from London to Manchester... Could a folding phone save Samsung? Firm patents radical... Artificial intelligence will'inevitably' destroy millions... Do YOU count on your fingers? Experts say it could actually...