For the first 3 or 4 charges the charger should be left connected and on for at least 16hrs [Nokia say you shouldn't leave it on more than a week (7 days)]. This sets up the battery so that it can take full charge in the future when you stick it in charge and it has finished in about 1hour.
Well it took more than a month to get the answers. It's too late now guys. And the 16 hours charging is not mentioned on my manual, and not on any phone manual i had. I have charged and discharged it for about three times 12-14hours just when i bought it,but it's duration is the same with the old one which i had just charged it and discharged it for 2-3 hours and only the first charge. The next few charges had lasted until i got the battery full message, but then i charged it again when the battery was fully discharged.