Diagnosis
The red triple-blink means the battery is completely dead and the charger isn't making a good connection. It's usually a simple connection issue, not a dead brush.
How to Fix It
Clean the charging contacts. First, unplug the charger from the wall. Use a dry cotton swab to firmly wipe the two small metal pins on the charger base. Then, wipe the two corresponding metal rings on the bottom of the brush handle. Plug the charger back in and place the brush firmly on the base.
If That Didn't Work
Try a different USB power source. The included glass charger must be plugged into a USB wall adapter that provides at least 1 amp. The brush won't charge from a low-power USB port on a computer or some power strips.
Heads Up
The glass charger is sensitive to moisture. If you've been storing the brush on it in a wet bathroom, water can bridge the contacts and prevent charging. Keep the base dry.