The battery provides approx 6V - the timing circuit uses a 555 IC to create a pulsed signal. The combination of resistor and capacitor values determines the period of oscillation. Then, the output signal from this circuit is used to switch a transistor on and off. That makes/breaks a connection from the battery to the LED strings.

I also added a switch to select between the red LED and Yellow LED strings.

Will draw the final circuit if I get some time :)