How do I know the status of the battery in my RP450c Reader? When the battery is fully charged, the red light on the device will remain illuminated. When the battery is at 10% or less, the Red light will blink intermittently on the device. Additionally, if the battery level is 15% or less, there is a visual indicator on the navigation bar indicating that the reader’s battery is low. For additional support, please refer to the Support Page in your merchant portal or contact your ISO contact.