Celebrating 80 years since the Royal Institution Christmas Lectures were first televised, chemist Professor Saiful Islam explores one of humankind's biggest challenges - how to generate and store energy, with guest appearances from Christmas Lecturers past. In the final lecture, Saiful explores one of the most important issues facing the modern world - how to store energy. He tackles his toughest challenge yet - trying to work out how to store enough energy to power a mobile phone for a whole year and still fit it in his pocket!