I have a 19.5 briggs and stratton motor. Starts sometimes won't starts others. Acts like the battery is dead, but it's not. New battery and starter. Negative and positive
Cables have been checked

Hi,
Two of the most failed parts on a mower are the solenoid and the key switch. In your case it sounds like the key switch is only making contact som of the times internally. An experiment would be to trying it repeatedly when you get a failure to start situation to see if it happens to make contact at one of those other times.
Peace,
Clarke