Batteries are large sheds used for the intensive rearing of chickens, a process which produces cheap protein but meat of poor flavour and texture. It is a grim business, for the birds are raised in vile conditions, crammed in cages the size of an A4 piece of paper and stacked in tiers from floor to ceiling. They do nothing except eat processed food and are kept in bright light 24 hours a day, so they never sleep. If the air-conditioning is not working, the ammoniacal stench defies description, while the din from the birds is deafening. At eight weeks they are jammed into crates to be transported to the abattoir, many arriving with broken legs and wings, some arriving dead. Slaughter involves being slung upside down on conveyor belts, which first dip their heads in electrically charged water to stun them before their necks are cut.