This is funny cause I was noticing this on my new 10.4.
If I am plugged into shore power the light is on. It doesn't matter if it is switched to store or use. But be careful, because if it is on store the light is on and the battery will not charge:).....
I would think the light would be an indicator of the battery being online.
Also, with the shore power hooked up, the led charge percent indicator will show full, even though the battery is discharged, just cause it is detecting the charger online.
Strange imo.