A red (or red & green) blinking light on the charger indicates that the battery is not charging.  You can try several things to actually troubleshoot the issue.  Please follow the steps below.  If any of the resulting steps corrects the issue, then no further action is required. Step 1: Remove the light from the charger, and then remove the battery from the light. This will reset the microprocessor (In most models). Reinstall the battery into the light and then reinsert the light into the charger. Always making sure the metal screws located in the neck of the light are making contact with the metal pins you see sticking out of the charger. Step 2:It may be due to the charging pins on the light being dirty.  Use a standard pencil eraser to clean the contacts on the light and then retest. In extreme cases where the light is very dirty use a toothbrush, soap, and water to clean the flashlights charging pins (IMPORTANT: Do not do this step on the charger itself as it is not waterproof.) Step 3: The problem may be with the charging cord itself.  If you are using the AC Charging cord and you also have the DC Charging cord, try connecting the charger to a DC outlet and see if that fixes the problem. If you originally had the issue while plugged into the DC Cord, try the supplied AC Charging Cord (if you have one). Step 4:  If you have an additional light of a similar model, try charging the same battery in a different light. If none of these steps correct the issue, please contact Customer Service for additional assistance.