Dual battery vehicle electrical systems

The invention provides a dual battery electrical switchable system for a vehicle having an engine. The vehicle comprises a plurality of first loads and a plurality of second loads The vehicle is switchable between an ON state in which the engine is running, an OFF state in which the engine is not running and a START state, in which at least one of the first loads requires power. The system comprises a first battery arranged to provide power to the first loads and a second battery arranged to provide power to the second loads A switch is provided between the first battery and the second battery and control means is arranged to open the switch only when the vehicle is in the OFF state. A connection system is also provided having a plurality of output terminals for connection to the plurality of primary and secondary loads and two input terminals for connection to the first and second batteries respectively.