I'd check to see if it has any kind of a charge at all when first installing it. Perhaps it needs a pre-charging of some sort.
I bought the extended battery for the SCH-U540 but when I place it in the phone the phone screen says "no battery." I thought maybe the battery was defective, so I exchanged it for another new one, but the phone still says "no battery." It seems that the phone does not recognize the extended battery, even though it is manufactured by Samsung and is the right model for the phone. Has anyone encountered this problem? Any suggestions on how to get the phone to recognize the battery?