Answer to: Back cover for the iPhone 4s the same as iPhone4?Be weary of clip placement on the back cover... there are certain points that it attaches to the housing; these points are different between the CDMA and GSM model iPhone 4s; at least one of the two will not work.
Answer to: When will you get a replacment iPhone 4S battery?According to the teardown so far, the connectors are different. You will need to purchase a specific battery for your iPhone 4. Be sure to investigate software as a culprit of poor battery life. A restore to factory settings will help troubleshoot this.