The usual method for implementing the low-battery warning featured in most battery-operated equipment is to illuminate an LED. By drawing current, however, the LED exacerbates the low-battery condition. You can greatly reduce the LED's power consumption by operating it at a low frequency and a low duty cycle. An existing low-battery output (LBO) like that found on DC-DC converters offers a convenient way to light the LED (Figure 1). IC1 is a small, inexpensive comparator with shutdown capability in a 6-pin SC70 package. It remains in shutdown while the battery voltage is at normal operating levels, but asserts LBO when battery voltage falls below a preset threshold.