Great little article tells how to drive one or more LEDs from old, dying batteries: http://www.edn.com/article/510577-LED_flashlight_circuit_works_at_voltages_as_low_as_0_5V.php This is the chip that does it (LT1932): http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1031,C1061,P2114