Isolating relay

Disconnect relay to protect the battery from discharging

The use of a cut-off relay is recommended for two main reasons: Firstly, it allows a battery to be charged while driving, and secondly, it protects the starter battery from discharging when the engine is switched off. An isolating relay only connects two batteries when the engine is running and the alternator is charging at the same time. An isolating relay is also necessary if two different battery types have been installed in the vehicle's on-board network, for example lithium (LTO or LiFePO4) and a lead AGM battery. As different battery types have equally different open-circuit voltages, this would lead to mutual discharge. This effect can be prevented with the help of a cut-off relay.