In this year's final Royal Institution Christmas Lecture, chemist Saiful Islam explores one of the most important issues facing the modern world - how to store energy. Over the course of the lecture, 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! With the UK generating nearly twenty times as much energy today as it did 80 years ago, finding better ways to store it is vital for all of our futures. Live experiments include an attempt to break the world record for the most powerful battery made of lemons and a clear-eyed look at the most energy-packed fuel in the world - hydrogen. Along the way Saiful investigates the chemistry of batteries and tells us what the future of energy has in store for us.