Battery of a laptop not charging

Hello,

I have a Dell Latitude D520 Laptop and it were all ok with it till last week,and now it's battery is not getting charged.The battery contact point with the computer gives only 3.29-3.30 DC Volt to charge tha battery.the battery icon is blinking read and green what is the matter and how can I find a solution for this?

The battery meter is showing 0% of charge

BIOS showing AC Adoptor :Unknown device installed what is the problem

Kindly help me