if you check, you will see the replacement has a different serial number and is a refurbished unit. MS doesn't replace batteries..
I've personally been escalating these battery issues all along (MVP's/Community Moderators are unpaid volunteers) and I've been begging for updates to be posted. I am a SP3 owner as well with the same issues.
update!
Well I couldn't stand it any longer. I finally decided to send my SP3 in and have the battery replaced. Got it back and it works great with a new simplo battery about 11 hrs of battery life with a 100% charge. I wish I could say that this forum provided any help or even comfort at all, but it didn't. I feel really let down by the MS team. It seems the moderators have no power to escalate anything to MS (and no desire to really do any troubleshooting) and MS doesn't really care about the users enough to update this thread with updates.
I Hope that MS identifies there is an issue with their product trouble escalation procedures, and can correct it. The SP3 is a great product, but the battery issue could've been a much less frustrating problem if MS got involved and communicated well to the consumers.
Hope the rest of you get an answer from MS soon. good luck.