From the service manual:
Battery Status Lights
If the computer is connected to an electrical outlet, the battery light operates as follows:
Alternately blinking amber light and blue light:
An unauthenticated or unsupported non-Dell AC adapter is attached to your laptop.
Alternately blinking amber light with steady blue light:
Temporary battery failure with AC adapter present.
Constantly blinking amber light:
Fatal battery failure with AC adapter present.
Light off:
Battery in full charge mode with AC adapter present.
Blue light on:
Battery in charge mode with AC adapter present.
Could be an adapter issue or a battery issue.
Casey