The exclamation mark usually means one of two things. You either waited too long to recharge your Charge and the battery is fully depleted. Or else an error occurred during a firmware update, in which case restarting your Charge and leaving it plugged in afterwards will cause the update to resume and complete.

How to Reset : Press the button on the charging cable 3 times within 8 seconds, briefly pausing between presses. The button is on the end of the charging cable that is plugged into the computer. 8 seconds after the first button press, the Fitbit logo appears on the tracker's display. This indicates that it has restarted.