Unni wrote:
I have a Craftsman Lawn tractor that needs to be jump started to get
going but used to run fine once it started. It will restart on its own
once it runs continuously for 10-15 minutes.

As of today, it shuts off if the jumper cable is removed. Could it be
alternator? the battery (possible shorted cells)? os something else?

Thanks a lot for your help.

How old is the battery? Batteries in mowers have hard lives and are only
good for a couple of years.

Take it to a mechanic who does mowers and small engines.