The battery charger comes with a red LED that will illuminate
or flash if a malfunction of the charger or battery
occurs.
One of the following may be the cause in the event of
charger failure and the red LED is blinking:


- AC mains failure
- DC fuse blown
- Power circuit break down
One of the following may be the cause in the event of battery failure and the red LED is ON:
- The total security time, 14 or 15 hours, has expired.
- The security time before the battery gassing voltage,
10 hours, has expired.
- The battery voltage is lower than 2.05V per cell after
one hour of charge.

Hope this helps understand why the battery charger light is flashing.
And what kevin_k said is also a possibility :o)