Plug in the charger and apply the charger cable to the Test Lamp. The charge time for a completely discharged battery is +/- 4 hours. Do not charge for more than 6 hours. The Test Lamp must be fully charged when stored immediately after use. Every 3 months the unit should be recharged when stored without using. During charging the red LED on the left of the test lamp is on. However, when the test lamp is completely discharged, during the first hours the red LED may be off.