My Samsung duos s 7582 is getting discharged very quickly in about a minute when the battery percentage shows in between 25 to 30 %. When the battery is fully charged it runs the mobile for 8 to 10 hours till the battery shows 30 % . But after that battery gets discharge in a minute.
It might be because of an old battery, did you buy a new battery to test it, otherwise you can go to any good repair shop to test it and to get a new battery.
Otherwise the battery might be bad calibrated. You need root to try to calibrate. Here is one of the many links to the many apps.