DIAGNOSIS The battery is not communicating with the tool. The red flashing light on the battery indicator signals a communication fault between the battery and the tool's electronic controller.
FIX First, perform a hard reset on the battery. Remove the battery from the drill. Press and hold the battery's fuel gauge button for 10-15 seconds. This discharges any residual power. Reinstall the battery firmly into the tool until it clicks. Test the trigger.
IF THAT DIDN'T WORK The fault may be dirty contacts. Inspect the metal terminals on both the battery and the drill. Clean them with a dry cloth or a pencil eraser to remove any oxidation or debris. Ensure the battery is fully seated and latched.
HEADS UP This error is specific to the HP (High Performance) battery system. A standard Ryobi ONE+ battery may not trigger this fault in the same way, but may also not provide full power to the HP brushless motor.