Red Dwarf Season 10 Episode 3

Marooned in Britain in 23 AD, the Dwarfers need an 8-volt battery to power up their Returner Remote and get home. Remembering a lesson from school, Rimmer suggests they make a battery out of lemons - but the nearest lemon to Britain in 23 AD is in India, 4,000 miles away. They begin their journey, a journey that will ultimately lead them to a meeting with a historical A List Celebrity that could alter the entire history of civilisation.