Automatic Battery Switchover

This circuit, which is designed for use with 6-V rechargeable batteries, provides automatic switchover to a reserve battery when the voltage of the main battery approaches the fully discharged level. The clever thing about this circuit is that the actual switchover is voltage-dependent and adjustable, even though the circuit essentially consists of only two components. The active element is a small thyristor (type BRX49), which is connected between the load and the reserve battery.