Even I was facing the same problem with my 3 year old Nokia N73 with 1 year old replaced battery.It used to get heated up abnormally and drained the entire battery within 15-20 minutes. Even during charging it used to get heated up and switched off automatically. Later I found that my memory card was not working and my phone was not able to access it. Then I removed it and checked my mobile for overheating. Now it is working fine without inserting that corrupted memory card.however i haven't checked it yet with a new memory card.
This was my experience which I liked to share in case anyone faces the same problem.