Battery not being recognized

I fully discharged my Latitude D820's battery. (Im using Xp, I had disabled all power warning options and let the battery completely run out).

After this, the battery is not getting charged. Or rather the battery is not getting recognized at all. The bios shows there is no primary battery.

Until this incident,the 5 months old battery was working perfectly well and would last about 3 hours.

But now it just seems dead all of a sudden. 

I had this same prob with my first battery that 'died' in an exactly similar way after 9 months of purchase.

At that time, I got this replacement battery(the one currently dead) .

On contacting tech support they are saying that I have to buy a new battery.

But it seems to me that the battery is not actually dead, but my laptop is not recognising it.(Was working at near 100% efficiency just before the prob, same case with the earlier battery too).