This 18-volt NiCad battery charger is compatible with various makes and models of hand-held power tools and is sold as an individual charger. When the charger is connected to the wall outlet and your battery is plugged in, a single red-light will turn on, indicating it has begun charging. This light will stay on as long as the battery and...Read more charger are in contact ? it will not flash, turn off or change color. If you notice that the light does turn on when you connect your battery, check the charger wire for damage. It is also important that you replace your charger in the event that the cable frays, the charger interrupts or completely stops charging your batteries, or if the charger becomes excessively hot during the charging process.