It means the system doesn't detect a battery.

 

I have a DELL Inspiron 6400 (for one and half a year). Recentle I have had problem with the battery. Since the last time the battery depleted whenever I connect the AC addaptor to charge it, the battery indicator (the most right of 3 inds) lights for about a minute and then goes off and the battery seems not to be charging. The power meter shows the battery status as "remainig charge 0% (charging)". The hardware diagnosis returned error code 3600:0123 for charge circuit. Now it only works when the AC addaptor is connected. Could you please tell me whats wrong with my DELL?  Does the battery need to be replaced or the problem is with the main board?

Since the battery is near the end of its expected lifespan (18-24 months is normal), I'd try a new battery first.