My Sears 18 horse rider mower turns over but it does not seem to have enough power to turn the flywheel fast enough to start. The starter starts to get hot, and the battery goes down. When I jump it with my car, it does not make a difference. My question. Is it the starter or the battery? Thanks in advance for any advice.

Well if jumping to you car doesn't make any difference, it ain't yo battery. That doesn't mean its your starter. Any starter will get hot if you crank on it long enough. If mower doesn't start in 15-30 seconds must be something wrong with engine, not starter.