Normally when your battery gives way, its better to replace your set 'cause finding a substitute battery - that actually works - is all but a matter of luck and a process of trial and error...
When my phone's battery started to conk out, I tried a number of different batteries (at least 3-4 of them), but none of them were up to scratch - they would die down in a matter of hours because even when the phone would be showing full battery strength, a 3 min chat would render the battery dead in its tracks (you dont have any idea, or maybe you now have :P, as to how much frustrating it is..!!)...
Then one fine morning (ahemm..just to give it a bit of a dramatic twist :P), I ventured out in search of a battery that would at least last a couple of days without dying on me in the middle of my calls..!!! So I went up to this, then newly opened, shop and inquired if they stocked those particular batteries.. the reply was in the affirmative, and so I bought one battery off them and headed back home.. I tried the battery for a day or two, and to my utter surprise, it worked just like the original one, if not any better..!! damn, I was so excited that I went back to that shop a couple of days afterwards and bought two more batteries off them and they both worked perfectly fine just like the earlier one..!!
I get attached to my stuff very easily, so having those batteries meant, I still could have my Nokia 6510 working in perfect order that I bought in Karachi somewhere around 2001... I love my phone, and its still working..!!
Now if only you had been in Peshawar, I'd have given you the location of that shop.. at least you could have then given it a try.. and just for the record, the batteries just cost me ~200-300 something each (cant remember the exact figure but it was thereabouts)..