Acer Aspire D250 Battery issues?

I received an Acer Aspire D250-1026 Netbook from a friend a few days ago, brought it home plugged it in, started cleaning up the HDD and installing the latest drivers I could find for it, as I knew it had sat unused for a few months. I let it sit over night plugged into the ac adapter and all seemed fine until I unplugged it. Died instantly.

Searched forums looking for answers and saw quite a few issues with other Aspire one models in regards to Bios issues causing battery problems, so I found a Bios V1.27 for the D250 netbook and installed it, no change.

Works fine while plugged in, the battery LED remains a solid green the entire time, windows shows a 100% battery level and still unplugging it shuts it down instantly.

I'm sure its long out of warranty and since it was free to me the investment of a new battery wouldn't break my heart any. I'd just like to know if there are any other known issues with these units or if the new battery will solve the problem. I'd also like any suggestions on replacement batteries. It currently has the 3 cell one, are the 6 cell batteries reliable and are the 9 cell ones overkill?. Any thoughts/advice on this matter is appreciated.

Acer Aspire One D250-1026
Windows XP Home
1gb RAMM
160gb HDD

li-Ion batteries have the habit of losing some cells every time they are fully discharged. It sounds to me like this netbook went through quite a number of full discharges, and it won't surprise me if the battery is not capable of holding a charge any longer.
As far as the number of cells... it depends to what extent this netbook is going to be used unplugged. The more cells you have, the longer battery life/charge. Not an overkill, in my opinion.