WTB: HP nx7400 Laptop battery

I purchased my hp nx7400 battery from a store in uni center, karachi. But after 6 months the battery was dead. Not due to electricity fluctuation but may be due to its make. This was my second battery but it was made in china Rs 8,000/- with 3 days check warranty.

I want to purchase a new battery whether made in china or original HP. But it should be cheap, new and with 1 year warranty, can anyone suggest me a store in Karachi where i can get it. One of the famous HP dealer says Rs 8,000 for original HP battery but 8,000 is too costly.

Please help me !

This is my laptop :