This is a High Capactity and high quality replacement battery for your Samsung I9000 Galaxy S. As you know the phone is power hungry so why not keep a spare High Capacity battery with you.
For the first 15 days it worked fine, infact better then the original one. But gradually after that it started losing its capacity and after 30 days today it can go only upto 10-12 hours minimal use. Would advise this only as a backup in case of emergencies.
I bought this battery and have charged it and discharged it several times. It does not hold the charge as long as the original battery and lasts only a few hours of normal useage. So it was a waste for me.