As the Fitbit Flex charges each of the Flex’s LED indicator lights will pulse to show the battery level every few seconds. There are 5 lights on the Fitbit Flex so each one indicates 20% of battery charge.
To fully charge the Flex, it should take around 3 hours. When it’s charged, all 5 indicator lights will blink.
I will upload a video shortly showing how the Fitbit Flex appears once fully charged.