Model: MC637B

For some weeks now the battery life on my iPhone 3GS has become significantly reduced. I was then recently contacted by my mobile provider to let me know I was approaching my monthly data limit, which surprised me since I typically use very little mobile data.

Upon resetting my phone to the factory settings the problem disappeared, and it then reappeared only when I added my Hotmail account back. By further process of elimination I believe it is specifically the contacts syncing as the battery usage seemed less significant with only Mail or Calendar syncing enabled.

Is this a known problem? Could there be a corrupted contact that the phone is repeatedly trying to sync, or is the issue with my account?

Any help or advice would be greatly appreciated.